Observatories may be distinguished into public and private. A _private_

observatory may be comprehended in a comparatively small building, or

in the wing of a building of ordinary dimensions for a family, provided

the situation is adapted to it. Most of our densely-peopled towns

and cities, which abound in narrow streets and lanes, are generally

unfit for good observatories, unless at an elevated position at their

extremities. Public observatories, where a great variety of instruments

is used, and where different observers are employed, require buildings

of larger dimensions, divided into a considerable number of apartments.

The observatory of _Greenwich_ is composed principally of two separate

buildings--one of which is the observatory properly so called, where

the assistant lives and makes all his observations; the other is the

dwelling-house in which the astronomer-royal resides. The former

consists of three rooms on the ground-floor, the middle of which is

the assistant’s sitting and calculating room, furnished with a small

library of such books only as are necessary for his computations, and

an accurate clock made by the celebrated Graham, which once served Dr.

Halley as a transit-clock. Immediately over this is the assistant’s

bed-room, with an alarum to awake him to make his observations at

the proper time. The room on the eastern side of this is called the

_transit_-room, in which is an 8 feet transit instrument, with an

axis of 3 feet, resting on 2 pieces of stone, made by Mr. Bird, but

successively improved by Messrs. Dollond, Troughton and others. Here

is also a chair to observe with, the back of which lets down to any

degree of elevation that convenience may require. On the western side

is the _quadrant room_, with a stone pier in the middle running north

and south, having on its eastern face a mural quadrant of 8 feet

radius, by which observations are made on the southern quarter of the

meridian, through an opening in the roof, of 3 feet wide, produced by

means of two sliding shutters. On the western face is another mural

quadrant of 8 feet radius, the frame of which is of iron, and the arch

of brass, which is occasionally applied to the north quarter of the

meridian. In the same room is the famous zenith sector, 12 feet long,

with which Dr. Bradley made the observations which led to the discovery

of the nutation of the earth’s axis and the aberration of the light

of the fixed stars. Here are also Dr. Hooke’s reflecting quadrant and

three time-keepers by Harrison. On the south side of this room a small

wooden building is erected for the purpose of observing the eclipses

of Jupiter’s satellites, occultations of stars by the moon, and other

phenomena which require merely the use of a telescope, and the true

or mean time. It is furnished with sliding shutters on the roof and

sides to view any part of the hemisphere from the Prime Vertical down

to the southern horizon. It contains a 40-inch achromatic, with a

triple object-glass; and also a 5 feet achromatic by Messrs. John and

Peter Dollond--a 2 feet reflecting telescope by Edwards, and a 6 feet

reflector by Herschel. Above the dwelling-house is a large octagonal

room, which is made the repository for certain old instruments, and for

those which are too large to be used in the other apartments. Among

many other instruments, it contains an excellent 10 feet achromatic by

Dollond, and a 6 feet reflector by Short. Upon a platform, in an open

space, is erected the great reflecting telescope constructed by Mr.

Ramage of Aberdeen, on the Herschelian principle, which has a speculum

of 15 inches diameter, and 25 feet focal length, remarkable for the

great accuracy and brilliancy with which it exhibits celestial objects.

Various other instruments of a large size, and of modern construction,

have of late years been introduced into this observatory, such as the

large and splendid transit instrument constructed by Troughton, in

1816--the two large _mural circles_ by Troughton and Jones--the transit

clock, by Mr. Hardy, and several other instruments and apparatus which

it would be too tedious to enumerate and describe.

Every observatory, whether public or private, should be furnished with

the following instruments. 1. A transit instrument for observing the

meridian passage of the sun, planets and stars. 2. A good clock whose

accuracy may be depended upon. 3. An achromatic telescope, at least

44 inches focal distance, with powers of from 45 to 180 for viewing

planetary and other phenomena--or, a good reflecting telescope at least

3 feet long, and the speculum 5 inches diameter. 4. An equatorial

instrument, for viewing the stars and planets in the day-time, and for

finding the Right Ascension and declination of a comet, or any other

celestial phenomenon. Where this instrument is possessed, and in cases

where no great degree of accuracy is required, the equatorial may be

made to serve the general purposes of a transit instrument.

A private observatory might be constructed in any house which has a

commanding view of the heavens, provided there is an apartment in it,

in which windows may be placed, or openings cut out fronting the north,

the south, the east and the west. The author of this work has a small

observatory erected on the top of his house, which commands a view of

20 miles towards the east, 30 miles towards the west, and north-west,

and about 20 miles towards the south, at an elevation of above 200 feet

above the level of the sea, and the banks of the Tay, which are about

half a mile distant. The apartment is 12-1/2 feet long by 8-1/2 wide,

and 8-1/2 feet between the floor and the roof. It has an opening on

the north by which observations can be made on the pole-star; a window

on the south by which the meridian-passages of the heavenly bodies may

be observed; another opening towards the east, and a fourth opening,

consisting of a door, towards the west. There is a pavement of lead

on the outside, all around the observatory-room, enclosed by a stone

parapet 3-1/2 feet high, the upper part of which is coped with broad

flat stones, in certain parts of which groves or indentations are made

for receiving the feet of the pedestal of an achromatic telescope,

which form a steady support for the telescope in the open air, when

the weather is calm and serene, and when observations are intended

to be made on any region of the heavens. By placing an instrument

on this parapet, it may be directed to any point of the celestial

canopy, except a small portion near the northern horizon, which is

partly intercepted by a small hill. In the following ground-plan, fig.

91. AAA, is the parapet surrounding the observatory-room; BBB, a walk

around it nearly 3 feet broad, covered with lead. O is the apartment

for the observatory, having an opening C to the north, another opening

D to the east, E is a window which fronts the south, and F is a door

fronting the west, by which an access is obtained to the open area on

the outside. GHI is an area on the outside towards the south, covered

with lead, 15 feet long from G to H, and 6-1/2 feet from E to I, from

which a commanding view of the southern, eastern and western portions

of the heavens may be obtained: _eeee_ are positions on the top of the

parapet where a telescope may be conveniently placed, when observations

are intended to be made in the open air. The top of this parapet is

elevated about 30 feet from the level of the ground. On the roof of

the observatory, about 12 feet above its floor, on the outside is a

platform of lead, surrounded by a railing, 6 feet by 5, with a seat,

on which observations either on celestial or terrestrial objects may

occasionally be made. K is a door or hatchway, which forms an entrance

into the observatory from the apartments below, which folds down, and

forms a portion of the floor.

[Illustration: _figure 91._]

In the perspective view of the building fronting the title-page, the

position and general aspect of the observatory-part of the building may

be more distinctly perceived.

In public observatories, where zenith or polar distances require to be

measured, it is necessary that there should be a dome, with an opening

across the roof and down the north and south walls. Should an altitude

or azimuth circle, or an equatorial instrument be used, they will

require a revolving roof with openings and doors on two opposite sides,

to enable an observer to follow a heavenly body across all the cardinal

points. The openings may be about 15 inches wide, and the roof needs

not be larger than what is requisite for giving room to the observer

and the instrument, lest its bulk and weight should impede its easy

motion. There have been various plans adopted for revolving domes.

Fig. 92 represents a section of the rotatory dome constructed at East

Sheen by the Rev. Dr. Pearson. This dome turns round on three detached

spheres of lignum vitæ, in a circular bed, formed partly by the dome,

and partly by the cylindrical frame-work, which surrounds the circular

room of 9 feet diameter. A section of this bed forms a square which the

sphere just fills, so as to have a small play to allow for shrinking;

and, when the dome is carried round, the spheres, having exactly

equal diameters of 4-1/4 inches each, when placed at equal distances

from one another, keep their relative places, and move together in a

beautifully smooth manner. These spheres act as friction rollers in

two directions at the four points of contact, in case any obstacle is

opposed to their progressive motion by the admission of dirt, or by

any change of figure of the wood that composes the rings of the dome,

and of the gang-way. No groove is here made, but what the weight of

the roof resting on the hard sphere occasions. The dome itself moves

twice round for the balls once, and has, in this way, its friction

diminished. The wood of this dome is covered by Wyatt’s patent copper,

one square foot of which weighs upwards of a pound; and the copper is

so turned over the nails that fix it at the parts of junction, that not

a single nail is seen in the whole dome. This covering is intended to

render the dome more permanent than if it had been made of wood alone.

At the observatory at Cambridge the dome is made chiefly of iron. In

the figure _a_, _a_ represents one of the two oblong doors that meet

at the apex of the cone, and a piece of sheet-copper bent over the

upper end of the door which shuts last, keeps the rain from entering at

the place of junction. The two halves of the dome are united by brass

rods passing through the door-cheeks of wainscot at _a_ and _a_ by

means of nuts that screw upon their ends, which union allows the dome

to be separated into two parts when there may be occasion to displace

it. The wooden plate _bb_, which appears in a straight line, is a

circular broad ring to which the covering wainscot boards are made fast

above the eaves, and _cc_ is a similar ring forming the wall-plate or

gang-way on which the dome rests and revolves.

[Illustration: _figure 92._]

[Illustration: _figure 92_*.]

Fig. 92* shows a small door that lies over the summit of the dome, and

may be separately opened for zenith observations; the rod of metal with

a ring at the lower end passing through it, serves to open and shut

this door, and at the same time carries upon its upper end a large ball

that falls back on the roof when the door is open, and keeps the door

in a situation to be acted upon by the hook of a handle that is used

for this purpose. The doors _aa_ being curved, are made to open in two

halves, the upper one being opened first, on account of its covering

the end of the other; and the observer may open one or two doors as may

best suit his purpose. The weight of this dome is such that a couple of

wedges, inserted by a gentle blow between the rings _bb_ and _cc_, will

keep it in its situation under the influence of the strongest wind.

It may not be improper to remark, that in all observatories, and in

every apartment where celestial observations are made, there should,

if possible, be a uniform temperature; and consequently a fire should

never be kept in such places, particularly when observations are

intended to be made, as it would cause currents of air through the

doors and other openings, which would be injurious to the accuracy of

observations. When a window is opened in an ordinary apartment where a

fire is kept, there is a current of heated air which rushes out at the

top, and a current of cold air which rushes in from below, producing

agitations and undulations, which prevent even a good telescope from

showing celestial objects distinct and well defined; and, I have no

doubt, that many young observers have been disappointed in their

views of celestial phenomena, from this circumstance, when viewing

the heavenly bodies from heated rooms in cold winter evenings; as the

aërial undulations before the telescope prevent distinct vision of such

objects as the belts of Jupiter, the spots of Mars, and the rings of

Saturn.

CHAPTER IV.

ON ORRERIES OR PLANETARIUMS.

An orrery is a machine for representing the order, the motions, the

phases, and other phenomena of the planets. Although orreries and

planetariums are not so much in use as they were half a century ago,

yet as they tend to assist the conceptions of the astronomical tyro in

regard to the motions, order, and positions of the bodies which compose

the solar system, it may not be inexpedient shortly to describe the

principles and construction of some of these machines.

The reason why the name _Orrery_ was at first given to such machines,

is said to have been owing to the following circumstance. Mr. Rowley,

a mathematical-instrument-maker, having got one from Mr. George

Graham, the original inventor, to be sent abroad with some of his own

instruments, he copied it and made the first for the Earl of Orrery.

Sir R. Steele, who knew nothing of Mr. Graham’s machine--thinking to

do justice to the first encourager, as well as to the inventor of such

a curious instrument, called it an _Orrery_, and gave Mr. Rowley the

praise due to Mr. Graham. The construction of such machines is not

a modern invention. The hollow sphere of Archimedes was a piece of

mechanism of this kind, having been intended to exhibit the motions

of the sun, the moon, and the five planets, according to the Ptolemaic

system. The next orrery of which we have any account was that of

Posidonius, who lived about 80 years before the Christian era, of which

Cicero says, ‘If any man should carry the sphere of Posidonius into

Scythia or Britain, in every revolution of which the motions of the

sun, moon and five planets, were the same as in the heavens, each day

and night, who in those barbarous countries could doubt of its being

finished--not to say actuated--by perfect reason?’ The next machine of

this kind, which history records, was constructed by the celebrated

Boethius, the Christian Philosopher, about the year of Christ 510--of

which it was said ‘that it was a machine pregnant with the universe--a

portable heaven--a compendium of all things.’ After this period, we

find no instances of such mechanism of any note till the 16th century,

when science began to revive, and the arts to flourish. About this time

the curious clock in Hampton Court Palace was constructed, which shows

not only the hours of the day, but the motions of the sun and moon

through all the signs of the zodiac, and other celestial phenomena.

Another piece of mechanism of a similar kind is the clock in the

cathedral of Strasburg, in which besides the clock part, is a celestial

globe or sphere with the motions of the sun, moon, planets and the

firmament of the fixed stars, which was finished in 1574.

Among the largest and most useful pieces of machinery of this kind, is

the great sphere erected by Dr. Long in Pembroke Hall in Cambridge.

This machine, which he called the _Uranium_, consists of a planetarium

which exhibits the motion of the earth and the primary planets, the

sun, and the motion of the moon round the earth, all enclosed within a

sphere. Upon the sphere, besides the principal circles of the celestial

globe, the Zodiac is placed, of a breadth sufficient to contain the

apparent path of the moon, with all the stars over which the moon

can pass, also the ecliptic, and the heliocentric orbits of all the

planets. The Earth in the planetarium has a moveable horizon, to which

a large moveable brass circle within the sphere may be set coincident,

representing the plane of the horizon continued to the starry heavens.

The horizons being turned round sink below the stars on the east side,

and make them appear to rise, and rise above the stars on the west

side, and make them appear to set. On the other hand, the earth and the

horizon being at rest, the sphere may be turned round to represent the

apparent diurnal motion of the heavens. In order to complete his idea

on a large scale, the Doctor erected a sphere of 18 feet diameter, in

which above 30 persons might sit conveniently, the entrance to which is

over the South Pole, by six steps. The frame of the sphere consists of

a number of iron meridians, the northern ends of which are screwed to

a large round plate of brass with a hole in the centre of it; through

this hole, from a beam in the ceiling, comes the north pole, a round

iron rod about three inches long, and which supports the upper part of

the sphere, to its proper elevation for the latitude of Cambridge, so

much of it as is invisible in England being cut off, and the lower or

southern ends of the meridians terminate on, and are screwed down to a

strong circle of oak 13 feet diameter, which, when the sphere is put in

motion, runs upon large rollers of lignum vitæ, in the manner that the

tops of some wind-mills turn round. Upon the iron meridians is fixed

a zodiac of tin painted blue, on which the ecliptic and heliocentric

orbits of the planets are drawn and the stars and constellations

traced. The whole is turned round with a small winch, with as little

labour as it takes to wind up a Jack, although the weight of the iron,

tin, and the wooden circle is above a thousand pounds. This machine,

though now somewhat neglected, may still be seen in Pembroke Hall,

Cambridge, where I had an opportunity of inspecting it in November,

1839. The essential parts of the machine still remain nearly in the

same state as when originally constructed in 1758.

The machine which I shall now describe is of a much smaller and less

complex description than that which has been noticed above, and may

be made for a comparatively small expense, while it exhibits, with

sufficient accuracy, the motions, phases, and positions of all the

primary planets, with the exception of the new planets, which cannot be

accurately represented on account of their orbits crossing each other.

In order to the construction of the Planetarium to which I allude, we

must compare the proportion which the annual revolutions of the primary

planets bear to that of the Earth. This proportion is expressed in the

following table, in which the first column is the time of the Earth’s

period in days; the second, that of the planets; and the third and

fourth are numbers very nearly in the same proportion to each other.

365-1/4 : 88 :: 83 : 20 for Mercury.

365-1/4 : 224-2/3 :: 52 : 32 for Venus.

365-1/4 : 687 :: 40 : 75 for Mars.

365-1/4 : 4332-1/2 :: 7 : 83 for Jupiter.

365-1/4 : 10759-1/3 :: 5 : 148 for Saturn.

365-1/4 : 30686 :: 3 : 253 for Uranus.

[Illustration: _figure 93._]

On account of the number of teeth required for the wheel which moves

Uranus, it is frequently omitted in Planetariums, or the planet is

placed upon the arbor which supports Saturn. If we now suppose a

spindle or arbor with six wheels _fixed_ upon it in an horizontal

position, having the number of teeth in each corresponding to the

numbers in the third column, namely the wheel AM (fig. 93.) of 83

teeth, BL of 52, CK of 50, for the earth, DI of 40, EH of 7, and FG

of 5; and another set of wheels moving freely about an arbor having

the number of teeth in the fourth column, namely AN of 20, BO of 32,

CP of 50--for the earth; DQ of 75, ER of 83, and FS of 148. Then, if

these two arbors of fixed and moveable wheels be made of the size,

and fixed at the distance here represented, the teeth of the former

will take hold of those of the latter, and turn them freely when the

machine is in motion. These arbors, with their wheels, are to be placed

in a box of a proper size, in a perpendicular position; the arbor of

fixed wheels to move in pivots at the top and bottom of the box, and

the arbor of the moveable wheels to go through the top of the box,

and having on the top a wire fixed, and bent at a proper distance

into a right angle upwards, bearing on the top a small round ball,

representing its proper planet. If then, on the lower part of the arbor

of fixed wheels, be placed a pinion of screw-teeth, a winch turning a

spindle with an endless screw, playing in the teeth of the arbor, will

turn it with all its wheels, and these wheels will turn the others

about with their planets, in their proper and respective periods of

time. For, while the fixed wheel CK moves its equal CP once round, the

wheel AM will move AN a little more than four times round, and will

consequently exhibit the motion of Mercury; the wheel EH will turn the

wheel ER about 1/12 round, representing the proportional motion of

Jupiter; and the wheel FG will turn the wheel FS, about 1/29.5 round,

and represent the motion of Saturn, and so of all the rest.

[Illustration: _figure 94._]

The following figure (fig. 94.) represents the appearance of the

instrument when completed. Upon the upper part of the circular box

is pasted a Zodiac circle divided into 12 signs, and each sign into

30 degrees, with the corresponding days of the month. The wheel-work

is understood to be within the box, which may either be supported by

a tripod, or with four feet, as here represented. The moon, and the

satellites of Jupiter, Saturn and Uranus, are moveable only by the

hand. When the winch W is turned, then all the primary planets are

made to move in their respective velocities. The ball in the centre

represents the Sun, which is either made of brass or of wood gilded

with gold.

By this Planetarium, simple as its construction may appear, a variety

of interesting exhibitions may be made and problems performed, which

may be conducive to the instruction of young students of astronomy. I

shall mention only a few of those as specimens.

1. When the planets are placed in their respective positions by means

of an Ephemeris or the Nautical Almanack, the relative positions of

those bodies in respect to each other, the quarters of the heavens

where they may be observed, and whether they are to be seen in the

morning before sun-rise or in the evening after sun-set, may be at

once determined. For example, on the 19th of December, 1844, the

_heliocentric_ places of the planets are as follows:--Uranus 2° Aries;

Saturn 8° 27´ of Aquarius; Jupiter 7° 4´ Aries; Mars 12° 45´ Libra;

the Earth 27° 46´ Gemini; Venus 29° 48´ Virgo; Mercury 7° 53´ Pisces.

When the planets are placed on the planetarium in these positions, and

the eye placed in a line with the balls representing the Earth and the

Sun, all those situated to the left of the sun are to the east of

him, and are to be seen in the evening, and those on the right, in the

morning. In the present case, Uranus, Saturn, Jupiter, and Mercury are

evening stars, and Mars and Venus can only be seen in the morning.

Jupiter is in an aspect nearly _quartile_, or 3 signs distant from the

sun, and Uranus is nearly in the same aspect. Saturn is much nearer the

sun, and Mercury is not far from the period of its greatest _eastern_

elongation. Mars is not far from being in a quartile aspect, _west_ of

the sun, and Venus is near the same point of the heavens, approaching

to the period of its greatest _western_ elongation, and consequently

will be seen before sun-rise as a beautiful morning star. Jupiter and

Uranus, to the east of the sun, appear nearly directly opposite to

Venus and Mars, which are to the west of the sun. The phase[47] of

Venus is nearly that of a half-moon, and Mercury is somewhat gibbous,

approaching to a half-moon phase. If, now, we turn the machine by the

winch till the Index of the earth point at the 8th of August, 1845, we

shall find the planets in the following positions:--Mars and Saturn are

nearly in opposition to the sun; Venus and Mercury are evening stars at

no great distance from each other, and Jupiter is a morning star. In

like manner if we turn the machine till the Index point to any future

months, or even succeeding years, the various aspects and positions of

the planets may be plainly perceived. When the planets are moved by the

winch, in this machine, we see them all _at once_ in motion around the

sun, with the same respective velocities and periods of revolution

which they have in the heavens. As the planets are represented in the

preceding positions, Mercury, Jupiter and Mars, are evening stars,

and Venus, Saturn, and Uranus, morning stars, if we suppose the earth

placed in a line with our eye and the sun.

2. By this instrument, the truth of the Copernican or Solar system is

clearly represented. When the planets are in motion, we perceive the

planets Venus and Mercury to pass both before and behind the sun, and

to have two conjunctions. We observe Mercury to be never more than

a certain angular distance from the sun, as viewed from the earth,

namely 27°; and Venus 47°. We perceive that the superior planets,

particularly Mars, will be sometimes much nearer to the earth than at

others, and therefore must appear larger at one time than at another,

as they actually appear in the heavens. We see that the planets cannot

appear from the earth to move with uniform velocity; for when nearest

they appear to move faster, and slower when most remote. We likewise

observe that the planets appear from the earth to move sometimes

_direct_, or from west to east, then become retrograde, or from east

to west, and between both to be _stationary_. All which particulars

exactly correspond with celestial observations. For illustrating these

particulars there is a simple apparatus represented by fig. 95, which

consists of a hollow wire with a slit at top which is placed over the

arm of Mercury or Venus at E. The arm DG represents a ray of light

coming from the planet at D to the earth at F. The planets being then

in motion, the planet D, as seen in the heavens from the earth at F,

will undergo the several changes of position, which we have described

above, sometimes appearing to go backwards and at other times forwards.

The wire prop, now supposed to be placed over Mercury at E, may

likewise be placed over any of the other planets, particularly Mars,

and similar phenomena will be exhibited.

[Illustration: _figure 95._]

This machine may likewise be used to exhibit the falsity of the

Ptolemaic system, which places the Earth in the centre, and supposes

the sun and all the planets to revolve around it. For this purpose, the

ball representing the Sun is removed, and placed on the wire or pillar

which supports the Earth, and the ball representing the Earth is placed

in the centre. It will then be observed, that the planets Mercury and

Venus, being both within the orbit of the sun, cannot at any time be

seen to go behind it, whereas, in the heavens we as often see them go

behind as before the sun. Again, it shows that as the planets move in

circular orbits about the central earth, they ought at all times to

appear of the same magnitude; while, on the contrary, we observe their

apparent magnitudes in the heavens to be very variable; Mars, for

example, appearing sometimes nearly as large as Jupiter, and at other

times only like a small fixed star. Again, it is here shown that the

planets may be seen at all distances from the sun; for example, when

the sun is setting, Mercury and Venus, according to this arrangement,

might be seen, not only in the south but even in the eastern quarter

of the heavens--a phenomenon which was never yet observed in any age;

Mercury never appearing beyond 27° of the Sun, nor Venus beyond 48°.

In short, according to the system thus represented, it is seen, that

the motions of the planets should all be regular, and uniformly the

same in every part of their orbits, and that they should all move the

same way, namely from west to east; whereas, in the heavens, they are

seen to move with variable velocities, sometimes appearing stationary,

and sometimes moving from east to west, and from west to east. All

which circumstances plainly prove that the Ptolemaic cannot be the true

system of the universe.

A Planetarium, such as that now described, might be constructed

with brass wheel-work, for about 5 guineas. The brass

wheel-work of one which I long since constructed cost about 3

guineas, and the other parts of the apparatus about 2 guineas

more. The following are the prices of some instruments of this

kind as made by Messrs. Jones, 30, Lower Holborn, London. ‘An

Orrery, showing the motions of the Earth, Moon, and inferior

planets, Mercury and Venus, by wheel-work, the board on which

the instrument moves being 13 inches diameter, £4: 14s. 6d.’ ‘A

Planetarium showing the motions of all the primary planets by

wheel-work with 1-1/2 inch or 3 inch papered globes,--according

to the wheel-work and the neatness of the stands, from £7:

17s. 6d. to £10: 10s.’ ‘Ditto, with wheel-work to show the

parallelism of the Earth’s axis, the motions of the Moon, her

phases, &c., £18: 18s.’ ‘Ditto, with wheel-work, to show the

earth’s diurnal motion, on a brass stand in mahogany case, £22:

1s.’ ‘A small _Tellurian_, showing the motion of the Earth and

Moon, &c., £1: 8s.’

HENDERSON’S PLANETARIUM.

The following is a description of the most complete and accurate

planetarium I have yet seen. The calculations occupied more than eight

months. For this article I am indebted to my learned and ingenious

friend Dr. Henderson, F.R.A.S., who is known to many of my readers by

his excellent astronomical writings.

[Illustration: _figure 96._]

Section of the wheel-work of a Planetarium for shewing with the utmost

degree of accuracy the mean tropical revolutions of the planets round

the sun, calculated by E. Henderson, LL.D. &c.

In the above section the dark horizontal lines represent the wheel-work

of the Planetarium, and the annexed numerals, the numbers of teeth in

the given wheel. The machine has three axes or arbors, indicated by

the letters A, B, C.--Axis ‘C,’ the ‘Yearly axis,’ is assumed to make

one revolution in 365.242,236 days, or, in 365 days 5^h 48^m 49.19^s

and is furnished with wheels 17, 44, 54, 36, 140, 96, 127, 86, which

wheels are all firmly riveted to said axis, and consequently they turn

round with it in the same time. Axle ‘B’ is a fixture; it consists

of a steel rod, on which a system of pairs of wheels revolve; thus

wheels 40 and 77 are made fast together by being riveted on the same

collet represented by the thick dark space between them, as also of

the rest: the several wheels on this axis may be written down thus;

40/77, 49/129, 20/94, 79/81, 30, 27/50, 41/65, 59/65, 96, 77/47, 67/42.

On axis A a system of wheels, furnished with tubes revolve, and these

tubes carry horizontal arms, supporting perpendicular stems with the

planets. The wheels on this axis are 173, 117/190, 111, 119, 122/130,

123/127, 83, 239, 96, 128, 72. From the following short description

the nature of their several actions will, it is presumed, be readily

understood--viz.,

[Sidenote: MERCURY’S PERIOD.]

On the axis ‘C’ at the bottom is wheel 86, which turns round in 365

days 5^h 48^m 49.19^s, this wheel impels a small wheel of 22 teeth, to

which is made fast to wheel 67, both revolving together at the foot

of axis B; wheel 67 drives a wheel of 72 once round in the period of

87 days, 23^h 14^m 36.1^s: this last mentioned wheel has a long tube,

which turns on the steel axis A, and carries a horizontal arm with the

planet Mercury round the sun in the time above noted.

[Sidenote: VENUS’S PERIOD.]

On axis ‘C’ is wheel 127, which drives wheel 47, to which is riveted a

wheel of 77 teeth, which impels a wheel of 128 teeth on axis A, and

causes it to make a revolution in 224 days, 16^h 41^m 31.1^s, and is

furnished with a tube, which revolves over that of Mercury and ascends

through the cover of the machine, and bears an arm on which is placed a

small ball representing this planet in the time stated.

[Sidenote: THE EARTH’S PERIOD.]

The motion of the earth round the sun is simply effected as

follows--the assumed value of axis ‘C;’ the ‘Yearly axis’ is 365 days

5^h 48^m 49.19^s; hence a system of wheels having the same numbers of

teeth, or at all events, the first mover, and last wheel impelled must

be equal in their numbers of teeth; in this machine three wheels are

employed, thus; a wheel having 96 teeth is made fast to the Yearly

axis C and of course moves round with it in a mean solar year, as

above noted, this wheel impels another wheel of 96 teeth, on axis B,

and this in its turns drives a third wheel of 96 teeth on axis A, and

is furnished with a long tube which revolves over that of Venus, and

ascends above the cover-plate of the machine, and bears a horizontal

arm which supports a small terrestrial globe, which revolves by virtue

of said wheels once round the sun in 365 days 5^h 48^m 49.19^s.

[Sidenote: MARS’ PERIOD.]

The revolution of this planet is effected as follows--a wheel of 140

teeth is made fast to the yearly axis C, and drives on axis B a wheel

of 65 teeth, to which is fixed a wheel of 59 teeth, which impels a

large wheel of 239 teeth on axis A once round the sun in 686 days

22^h 18^m 33.6^s, this last-mentioned wheel is also furnished with a

tube which revolves over that of the earth, and carries a horizontal

arm bearing the ball representing Mars, and causes it to complete a

revolution round the sun in the period named.

[Sidenote: _THE ASTEROIDS._ VESTA’S PERIOD.]

The period of Vesta is accomplished thus, viz. On the Yearly axis C,

is made fast a wheel of 36 teeth, which drives a wheel of 65 teeth on

axis B, to which is fixed a wheel of 41 teeth, which impels a wheel of

83 teeth on axis A, once round in 1336 days 0^h 21^m 19.8^s: The tube

of which last wheel ascends on that of Mars, and like the rest bears an

arm supporting a ball representing this planet.

[Sidenote: JUNO’S PERIOD.]

For the revolution of Juno, the yearly axis C is furnished with a wheel

of 54 teeth, which impels a wheel of 50 teeth on axis B, to which is

made fast a wheel of 27 teeth which turns a wheel of 127 teeth on axis

A, once round in 1590 days 17^h 35^m 2.7^s, and the tube of which

ascends on that of Vesta, and supports a horizontal arm which carries a

small ball representing this planet in the period named.

[Sidenote: CERES’ PERIOD.]

The revolution of Ceres is derived from the period of Juno, because

wheel-work taken from the unit of a solar year was not sufficiently

accurate for the purpose, therefore on Juno’s wheel of 127 teeth is

fixed a wheel of 123 teeth, which drives a thick little bevel sort

of wheel of 30 teeth on axis B: the reason of this small wheel being

bevelled is to allow its teeth to suit both wheels 123/130; wheel 30

drives wheel 130, on axis A once round in 1681 days, 6^h 17^m 22.4^s

and the tube of wheel 130 turns on the tube of Juno, and ascends in a

similar manner with the rest and carries an horizontal arm supporting a

small ball representing this planet, and is caused to revolve round the

Sun in the above mentioned period (the period of Ceres to that of Juno

is as 130 is to 123; hence the wheels used.)

[Sidenote: PALLAS’S PERIOD.]

The Period of Pallas could not be derived from the solar year with

sufficient accuracy, and recourse was had to an engrafted fraction on

the period of Ceres, thus. On wheel 130 of Ceres is made fast a wheel

of 122 teeth, which drives a wheel of 81 teeth on axis B, to which is

fixed a wheel 79 which impels a wheel of 119 teeth on axis A, and is

furnished with a tube which ascends, and turns on that of Ceres, and

supports a horizontal arm, which bears a small ball representing this

planet, which by virtue of the above train of wheels is caused to

complete a revolution round the Sun in 1681^d 10^h 28^m 25.1^s.

[Sidenote: JUPITER’S PERIOD.]

The motion of this planet is derived from the period of a solar year;

from the ‘yearly axis’ thus, on this axis is made fast a wheel of 44

teeth which turns a wheel of 94 teeth on axis B, to which is riveted

a small wheel of 20 teeth, which impels a wheel on axis A having 111

teeth, which is furnished with an ascending tube which revolves over

that of Pallas, and bears an horizontal arm which supports a ball

representing this planet, which by the said train of wheels is caused

to revolve round the Sun in 4330^d 14^h 39^m 35.7^s.

[Sidenote: SATURN’S PERIOD.]

The periodic revolution of Saturn is also taken from the solar

year--viz., a small wheel of 17 teeth is fixed to the ‘yearly axis’

near its top, and drives a wheel of 129 teeth on axis B, to which is

made fast a wheel of 49 teeth, which turns a wheel of 190 teeth on

axis A, whose tube ascends and revolves on that of Jupiter’s tube, and

supports an arm, having a ball representing Saturn and its rings, and

which by the train of wheels is caused to perform a revolution round

the sun in the period of 10746^d 19^h 16^m 50.9^s.

URANUS’S PERIOD.

The revolution of this planet could not be attained with sufficient

accuracy from the period of a solar year--the period is engrafted on

that of Saturn’s, thus, a wheel of 117 teeth is made fast to wheel 190

of Saturn, and consequently revolves in Saturn’s period. This wheel

of 117 teeth drives a wheel on axis B, having 77 teeth, to which is

fixed a wheel of 40 teeth, which turns on axis A, a large wheel of 173

teeth, whose tube ascends and revolves over that of Saturn, and carries

a horizontal arm which supports a ball representing this planet, which

is caused to complete its revolution by such a train of wheels in the

period of 30589^d 8^h 26^m 58.4^s. Such is a brief description of the

motions of this comprehensive and very accurate machine.

The axis A, on which the planetary tubular wheels revolve, performs

a rotation in 25 days 10 hours, by virtue of the following train of

wheels, 61/14 + 70/12 of 24 hours, that is, a pinion of 14 is assumed

to revolve in 24 hours, and to drive a wheel of 61 teeth, to which is

fixed a pinion of 12, which turns the wheel 70 in the period noted; to

this wheel-axis, it is made fast, and by revolving with it, exhibits

the Sun’s rotation.

[Sidenote: DIURNAL HAND.]

The machine is turned by a handle or winch, which is assumed to turn

round in 24 hours, and from this rotation of 24 hours a train of

wheel-work is required to cause the ‘yearly axis’ C, to turn once

round in 365^d 5^h 48^m 49.19^s, which is effected in the following

manner--viz, the train found by the process of the reduction of

continuous fractions is 61/14 + 144/18 + 211/23 that is, in the train

for turning the sun, the same pinion 14 turns the same wheel 61,

and turns a pinion of 18 leaves, to which is fixed a wheel of 144

teeth, having a pinion of 23 leaves, which impels a large wheel of

241 teeth once round in 365.242236^d or 365^d 5^h 48^m 49.19^s, this

last-mentioned wheel of 241 teeth is made fast to the under part of

the ‘yearly axis’ C at D, the handle having a pinion of 14 leaves

therefore, and transmitting its motion through the above train, causes

the yearly axis to revolve in the same period.

[Sidenote: REGISTRATING DATES.]

The planetarium is also furnished with a system of wheels for

registrating dates for either 10,000 years past or to come, the

arrangement is not shewn in the engraving (to prevent confusion) but

it might be shortly described thus:--Near the top of the yearly axis

is a hooked piece _e_, which causes the tooth of a wheel of 100 teeth

to start forward yearly, consequently 100 starts of said wheel will

cause it to revolve in 100 solar years, and it has a hand which points

on a dial on the cover of the machine the years; thus for the present

year this hand will be over the number 45. This last-named wheel of

100 teeth has a pin which causes a tooth of another wheel of 100 teeth

to start once in 100 years, hence this last wheel will complete one

revolution in 10,000 years, and it is for this purpose the former index

or hand moves over a number yearly. The second index will pass over a

number every 100 years--for the present year the second hand or index

will be over the number 18, and will continue over it until the first

index moves forward to 99, then both indexes will move at one time,

viz., the first index to 00 on the first concentric circle of the

dial, and the second index to 19, denoting the year 1900, and so of

the rest. By the ecliptic being divided in a series of four spirals,

the machine makes a distinction between common and leap years, and

indicates the common year as containing 365 days, and the leap-year 366

days, by taking in a day in February every fourth year; thus for any

given period for 10,000 years past or to come, the various situations

and aspects of the planets may be ascertained by operating with this

machine, and this for thousands of years without producing a sensible

error either in space or time. This planetarium wheel-work is enclosed

in an elegant mahogany box of twelve sides--is about 5 feet in diameter

by 10 inches in depth; at each of the twelve angles, or sides, small

brass pillars rise and support a large Ecliptic circle on which are

engraven the signs, degrees and minutes of the Ecliptic--the days of

the month, &c. This mahogany box with the wheel-work is supported by a

tripod stand three feet in height, and motion is communicated to the

several balls representing the planets by turning the handle as before

described. A Planetarium of this complicated sort, costs sixty guineas.

The following is a tabular view of the wheel-work, periods, &c.

----------+-----------------------------+---------------------+------------------

Planets’ | Wheel-work. | Tropical periods |True mean Tropical

Names. | | produced by the | Periods of

| | wheel-work. | the Planets.

----------+-----------------------------+---------------------+------------------

| | da. ho. m. s. | da. ho. m. s.

| | |

Mercury | 22/85 + 67/72 of a Year | 87. 23. 14. 36.1 | 87. 23. 14. 36

| | |

Venus | 47/127 + 128/77 " | 224. 16. 41. 31.1 | 224. 16. 41. 36

| | |

The Earth | Prime mover 96 + 96 + 96 " | 365. 5. 48. 49.19| 365. 5. 48. 49

| | |

Mars | 65/140 + 239/59 " | 686. 22. 18. 33.6 | 686. 22. 18. 34

| | |

Vesta | 65/36 + 83/41 " | 1335. 0. 21. 19.8 | 1335. 0. 21. 20

| | |

Juno | 50/54 + 127/27 " | 1590. 17. 35. 2.7 | 1590. 17. 35. 1

| | |

Ceres | 130/123 + 30 of Juno | 1681. 6. 17. 22.4 | 1681. 6. 17. 29

| | |

Pallas | 81/122 + 119/79 of Ceres | 1681. 10. 28. 25.1 | 1681. 10. 28. 42

| | |

Jupiter | 94/44 + 111/20 of a Year | 4330. 14. 39. 35.7 | 4330. 14. 39. 32

| | |

Saturn | 129/17 + 190/49 " | 10746. 19. 16. 50.9 |10746. 19. 16. 52

| | |

Uranus | 77/117 + 173/40 of Saturn | 30589. 8. 26. 58.4 |30589. 8. 26. 59

----------+-----------------------------+---------------------+------------------

The Sun’s 61/14 + 70/12 of 24 ho. | 25. 10. 0. 0 | 25. 10. 0. 1

Rotation | |

The tropical} 61/14 + 144/18 + 241/23 "| 365. 5. 48. 49.19| 365. 5. 48. 49

period of } | |

the Earth } | |

roundthe } | |

Sun. } | |

----------------------------------------+---------------------+------------------

In the month of October last year, Dr. Henderson made a series of

calculations for a new Planetarium for the use of schools. It shows

with considerable accuracy for 700 days, the mean tropical revolutions

of the Planets round the sun--the machine consists of a system of brass

wheels peculiarly arranged, and is enclosed in a circular case three

feet in diameter, the top of which has the signs and degrees of the

ecliptic laid down on it, as also the days of the months, &c. This

Planetarium costs only 45s. or on a tripod stand, table-high, 55s.; the

machine is put in motion by a handle on the outside. To the teachers

and others connected with education this Planetarium must be of great

importance, for without a proper elucidation of the principles of

astronomy, that of Geography must be but confusedly understood. This

Planetarium is at present made by Mr. Dollond, 9, White Conduit Grove,

Islington, London.

The _Tellurian_ is a small instrument which should be used in

connection with the Planetarium formerly described. This instrument is

intended to show the annual motion of the earth, and the revolution

of the moon around it. It also illustrates the moon’s phases, and the

motion of her nodes, the inclination of the Earth’s axis, the causes

of eclipses, the variety of seams, and other phenomena. It consists of

about eight wheels, pinions and circles. A small instrument of this

description may be purchased for about one pound eight shillings, as

stated in the note, page 527.

ON THE VARIOUS OPINIONS WHICH WERE ORIGINALLY FORMED OF SATURN’S RING.

[Illustration: _figure 97._]

The striking and singular phenomenon connected with the planet

Saturn--though now ascertained beyond dispute to be a Ring, or Rings,

surrounding its body at a certain distance--was a subject of great

mystery, and gave rise to numerous conjectures and controversies, for

a considerable time after the invention of the telescope by which it

was discovered. Though it was first discovered in the year 1610, it

was nearly 50 years afterwards, before its true form and nature were

determined. Galileo was the first who discovered anything uncommon

connected with Saturn: through his telescope he thought he saw that

planet appear like two smaller globes on each side of a larger one; and

after viewing the planet in this form for two years, he was surprised

to see it becoming quite round, without its adjoining globes, and

some time afterwards to appear in the triple form. This appearance

is represented in fig. 1 of the above engraving. In the year 1614,

Scheiner, a German astronomer, published a representation of Saturn,

in which this planet is exhibited as a large central globe, with two

smaller bodies, one on each side, partly of a conical form, attached to

the planet and forming a part of it, as shown fig. 2. In the year 1640

and 1643, Ricciolus, an Italian mathematician and astronomer, imagined

he saw Saturn as represented in fig. 3. consisting of a central

globe, and two conical shaped bodies completely detached from it, and

published an account of it corresponding to this view. Hevelius, the

celebrated astronomer of Dantzig, author of the _Selenographia_ and

other works, made many observations on this planet about the years

1643, 1649 and 1650, in which he appears to have obtained different

views of the planet and its appendages, gradually approximating to the

truth, but still incorrect. These views are represented in figures

4, 5, 6, and 7. Fig. 4 nearly resembles two hemispheres, one on each

side of the globe of Saturn. The other figures very nearly resemble

the extreme parts of the ring as seen through a good telescope, but

he still seems to have considered them as detached from each other as

well as from Saturn. Figures 8 and 9 are views given by Ricciolus at a

period posterior to that in which he supposed Saturn and his appendages

in the form delineated in fig. 3. In these last delineations the

planet was supposed to be enclosed in an elliptical ring, but this ring

was supposed to be _fixed_ to its two opposite sides.

Fig. 10, is a representation by Eustachius Divini, a celebrated

Italian optician at Bologna. The shades represented on Saturn and the

elliptical curve are incorrect, as this planet presents no such shadowy

form. The general appearance here presented is not much unlike that

which the ring of Saturn exhibits, excepting that at the upper side the

ring should appear covering a portion of the orb of Saturn. But Divini

seems to have conceived that the curve on each side was attached to the

body of Saturn. For when Huygens published his discovery of the ring

of Saturn in 1659, Divini contested its truth, because he could not

perceive the ring through his own telescopes; and he wrote a treatise

on the subject in opposition to Huygens, in 1660, entitled ‘Brevis

Annotatio in Systema Saturninum.’ Huygens immediately replied to him,

and Divini wrote a rejoinder in 1661.--Fig. 11 is the representation

given by Francis Fontana, a Neapolitan astronomer. This figure

represents Saturn as having two crescents, one on each side, attached

to its body, with intervals between the planet and the crescents. Fig.

12 is a view delineated by Gassendus, a celebrated French philosopher.

It represents the planet as a large ellipsoid, having a large circular

opening near each end, and, if this representation were the true one,

each opening would be at least 30,000 miles in diameter. Fig. 13,

which is perhaps the most singular of the whole, is said to be one

of the view’s of this planet given by Ricciolus. It represents two

globes--each of which, in the proportion they here bear to Saturn, must

be more than thirty thousand miles in diameter. These globes, were

conceived as being attached to the body of Saturn by curves or bands,

each of which, in the proportion represented, must have been at least

7000 miles in breadth, and nearly 40,000 miles long. This would have

exhibited the planet Saturn as a still more singular body than what

we have found it to be; but no such construction of a planet has yet

been found in the universe, nor is it probable that such a form of a

planetary body exists.

It is remarkable that only two general opinions should have been

formed respecting the construction of Saturn--as appears from these

representations--either that this planet was composed of three distinct

parts, separate from each other,--or that the appendage on each side

was _fixed_ to the body of the planet. The idea of a ring surrounding

the body of the planet, at a certain distance from every part of it,

seems never to have been thought of till the celebrated Huygens, in

1655, 1656 and 1657, by numerous observations made on this planet,

completely demonstrated that it is surrounded by a solid and permanent

ring, which never changes its situation, and, without touching the

body of the planet, accompanies it in its revolution around the sun.

As the cause of all the erroneous opinions above stated was owing to

the imperfection of the telescopes which were then in use, and their

deficiency in magnifying power,--this ingenious astronomer set himself

to work in order to improve telescopes for celestial observations. He

improved the art of grinding and polishing object-glasses, which he

finished with his own hands, and produced lenses of a more correct

figure, and of a longer focal distance than what had previously been

accomplished. He first constructed a telescope 12 feet long, and

afterwards one 23 feet long, which magnified about 95 times; whereas

Galileo’s best telescope magnified only about 33 times. He afterwards

constructed one 123 feet long, which magnified about 220 times. It was

used without a tube, the object-glass being placed upon the top of a

pole and connected by a cord with the eye-piece. With such telescopes

this ingenious artist and mathematician discovered the fourth satellite

of Saturn, and demonstrated that the phenomenon, which had been so

egregiously misrepresented by preceding astronomers, consisted of an

immense ring surrounding the body, and completely detached from it. His

numerous observations and reasonings on this subject were published

in Latin, in 1659, in a quarto volume of nearly 100 pages, entitled

‘_Systema Saturnium, sive de causis mirandorum Saturni Phenomenôn, et

Comite ejus Planeta Nova_,’ from which work the figures and some of the

facts stated above have been extracted.

ON THE SUPPOSED DIVISIONS OF THE EXTERIOR RING OF SATURN.

From the period in which Huygens lived till the time when Herschel

applied his large telescopes to the heavens, few discoveries were made

in relation to Saturn. Cassini, in 1671, discovered the fifth satellite

of this planet; in 1672, the third; and the first and second in March,

1684. In 1675, Cassini saw the broad side of its ring bisected quite

round by a dark elliptical line, of which the inner part appeared

brighter than the outer. In 1722, Mr. Hadley, with his 5 feet Newtonian

Reflector observed the same phenomenon, and perceived that the dark

line was stronger next the body, and fainter towards the upper edge

of the ring. Within the ring he also discovered two belts across the

disk of Saturn. But it does not appear that they had any idea that this

dark line was empty space separating the ring into two parts. This

discovery was reserved for the late Sir W. Herschel, who made numerous

observations on this planet, and likewise ascertained that the ring

performs a revolution round the planet in ten hours and thirty minutes.

Of late years, some observers have supposed that the exterior ring

of Saturn is divided into several parts, or, in other words, that it

consists of two or more concentric rings. The following are some of

the observations on which this opinion is founded. They are chiefly

extracted from Captain Kater’s Paper on this subject, which was read

before the Astronomical Society of London.

The observations, we are told, were made in the years 1825 and 1826,

and remained unpublished, from a wish on the part of the observer

to witness the appearances again. The planet Saturn has been much

observed by Captain Kater, for the purpose of trying the light, &c.,

for which the ring and satellites are good tests. The instruments

which were employed in the present investigations were two Newtonian

Reflectors--one by Watson, of 40 inches focus and 6-1/4 aperture; and

another by Dollond, of 68 inches focus, and 6-3/4 aperture. The first,

under favourable circumstances, gave a most excellent image, the latter

is a very good instrument. The following are extracts from the author’s

journal.

_Nov. 25, 1825._--The double ring beautifully defined, perfectly

distinct all around, and the principal belts well seen. I tried many

concave glasses, and found that the image was much sharper than with

convex eye-glasses, and the light apparently much greater. Dollond,

259, the best power, 480, a single lens, very distinct. _Nov. 30_, the

night very favourable, but not equal to the 25th. The exterior ring

of Saturn is not so bright as the interior, and the interior is less

bright close to the edge next the planet. The inner edge appears more

yellow than the rest of the ring, and nearer in colour to the body

of the planet. _Dec. 17_.--The evening extremely fine. With Dollond,

I perceived the outer ring of Saturn to be darker than the inner,

and the division of the ring all around with perfect distinctness;

but with Watson I fancied that I saw _the outer ring separated by

numerous dark divisions extremely close, one stronger than the rest,

dividing the ring about equally_. This was seen with my most perfect

single eye-glass power. A careful examination of some hours confirmed

this opinion.--_Jan. 16_ and 17, 1826.--Captain Kater believed that

he saw the divisions with the Dollond, but was not positive. Concave

eye-glasses found to be superior to convex. _Feb. 26, 1826_.--The

division of the outer ring not seen with Dollond. On the 17th Dec.,

when the divisions were most distinctly seen, Captain Kater made a

drawing of the appearance of Saturn and his rings. The phenomena

were witnessed by two other persons on the same evening, one of whom

saw several divisions in the outer ring, while the other saw one

middle division only; but the latter person was short-sighted, and

unaccustomed to telescopic observations. It may be remarked, however,

that these divisions were not seen on other evenings, which yet were

considered very favourable for distinct vision.

It is said that the same appearances were seen by Mr. Short, but the

original record of his observations cannot be found. In Lalande’s

_Astronomy_ (3rd edition, article 3351,) it is said, ‘Cassini remarked

that the breadth of the ring was divided into two equal parts by a

dark line having the same curvature as the ring, and the _exterior_

portion was the less bright. Short _told_ me that he observed still

more singular phenomena with his large telescope of 12 feet. The

breadth of the ansæ, or extremities of the ring; was, according to him,

divided into two parts,--an inner portion without any break in the

illumination, and an outer divided by several lines concentric with the

circumference; which would lead to a belief, _that there are several

rings in the same plane_.’ De Lambre and Birt severally state that

Short saw the outer ring divided, probably on the authority of Lalande.

In Brewster’s _Ferguson’s Astronomy_, vol. ii, p. 125, 2nd edition,

there is the following note on this subject. ‘Mr. Short assures us,

that with an excellent telescope, he observed the surface of the ring

divided by several dark concentric lines, which seem to indicate a

number of rings proportional to the number of dark lines which he

perceived.’

In Dec. 1813, at Paris, Professor Quetelet saw the outer ring divided

with the achromatic telescope of 10 inches aperture, which was

exhibited at the exposition. He mentioned this the following day to M.

de la Place, who observed, that ‘those or even more divisions, were

conformable to the system of the world.’ On the other hand the division

of the outer ring was not seen by Sir W. Herschel in 1792, nor by Sir

J. Herschel in 1826, nor by Struve in the same year; and on several

occasions when the atmospheric conditions were most favourable, it

has not been seen by Captain Kater. It has been remarked by Sir W.

Herschel, Struve and others, that the exterior ring is much less

brilliant than the interior. And it is asked, may not this want of

light in the outer ring arise from its having a very dense atmosphere?

and may not this atmosphere in certain states admit of the divisions

of the exterior ring being seen, though, under other circumstances,

they remain invisible? The above observations are said to have been

confirmed by some recent observations by Decuppis at Rome, who

announced, some years ago, that Saturn’s outer ring is divided into two

or three concentric rings.

Some of the observations stated above, were they perfectly correct,

would lead to the conclusion that Saturn is encompassed with a number

of rings, concentric with and parallel to each other. But while such

phenomena as described above are so seldom seen, even by the most

powerful telescopes and the most accurate observers, a certain degree

of doubt must still hang over the subject; and we must suspend our

opinion on this point, till future observations shall either confirm

or render doubtful those to which we have referred. Should the Earl

of Rosse’s great telescope, when finished for observation, be found

to perform according to the expectations now entertained, and in

proportion to its size and quantity of light, we shall expect that our

doubts will be resolved in regard to the supposed divisions of the ring

of Saturn.

APPENDIX.

BRIEF DESCRIPTION OF THE EARL OF ROSSE’S TELESCOPE.

This telescope, the largest and most magnificent that ever was

attempted, reflects the greatest honour on the genius, the inventive

powers, and the scientific acquirements of its noble contriver, as

well as on the elevated station in which he is placed. With rank and

fortune, and every circumstance that usually unfit men for scientific

pursuit, he has set a bright example to his compeers of the dignity and

utility of philosophical studies and investigations, and of the aids

they might render to the progress of science, were their wealth and

pursuits directed in a proper channel.

Previously to his Lordship’s attempting the construction of his

largest--or ‘Monster Telescope,’ he had constructed one with a speculum

of 3 feet in diameter, which was considered one of the most accurate

and powerful instruments that had ever been made, not excepting even

Sir W. Herschel’s forty-feet Reflector. In the account of this

telescope, published in the Philosophical Transactions for 1840,

his Lordship speaks of the possibility of a speculum of six feet in

diameter being cast. At that time, it was considered by some as little

short of a chimera to attempt the construction of such a monstrous

instrument. But the idea no sooner occurred to this ingenious and

persevering nobleman than he determined to put it to the test, and the

result has been attended with complete success. The materials of which

this speculum is composed are _copper_ and _tin_, united very nearly

in their atomic proportions, namely, copper 126.4 parts, to tin 58.9

parts. This compound has a specific gravity of 8.8, and it is found to

preserve its lustre with more splendor, and to be more free from pores

than any other. A foundry was constructed expressly for the purpose of

casting the speculum. Its chimney built from the ground was 18 feet

high, and 16-1/2 square at the base, tapering to four at the top. At

each of its sides, communicating with it by flue, was sunk a furnace

8 feet deep, and 5-1/2 square, with a circular opening 4 feet in

diameter. About seven feet from the chimney was erected a large crane,

with the necessary tackle for elevating and carrying the crucibles from

the furnace to the mould, which was placed in a line with the chimney

and crane, and had three iron baskets supported on pivots hung round

it; and four feet farther on was the annealing oven. The crucibles

which contained the metal were each 2 feet in diameter, 2-1/2 deep,

and together weighed one ton and a half; they were of cast iron and

made to fit the baskets at the side of the mould. These baskets were

hung on wooden uprights or pivots, to one of these on each side was

attached a lever, by depressing which it might be turned over, and

the contents of the crucible poured into the mould. The bottom of the

mould was made by binding together tightly layers of hoop-iron, and

turning the required shape on them edgewise. This mould conducted the

heat away through the bottom, and cooled the metal towards the top in

infinitely small layers, while the interstices, though close enough to

prevent the metal from escaping, were sufficiently open to allow the

air to penetrate. This bottom was six feet in diameter and 5-1/2 inches

thick, and was made perfectly horizontal by means of spirit levels, and

was surrounded by a wooden frame; a wooden pattern, the exact size of

the speculum, being placed on the iron; sand was well packed between

it and the frame, and the pattern was removed. Each of the crucibles

containing the melted metal was then placed in its basket, and every

thing being ready for discharging their contents, they were at the same

instant turned over, and the mould being filled, the metal in a short

time safely set into the required figure. Whilst it was red hot, and

scarcely solid, the frame-work was removed, and an iron ring connected

with a bar which passed through the oven, being placed round it, it

was drawn in by means of a capstan at the other side, on a railroad,

when charcoal being lighted in the oven, and turf fires underneath

it, all the openings were built up, and it was left for sixteen weeks

to anneal. It was cast on the 13th of April, 1842, at 9 o’clock in

the evening. The crucibles were ten hours heating in the furnaces

before the metal was introduced, which in about ten hours more was

sufficiently fluid to be poured. When the oven was opened the speculum

was found as perfect as when it entered it. It was then removed to the

grinding machine, where it underwent that process, and afterwards was

polished, without any accident having occurred.

This speculum weighed _three tons_, and lost about one eighth of

an inch in grinding. Lord Rosse has since cast another speculum of

the same diameter four tons in weight. He can now, with perfect

confidence, undertake any casting, so great an improvement has the

form of mould which he has invented proved. The speculum was placed

on an equilibrium bed, composed of nine pieces resting on points at

their centres of gravity; the pieces were lined with pitch and felt,

before the speculum was placed on them. The speculum box is also lined

with felt and pitched; this prevents any sudden change of temperature

affecting the speculum by means of the bad conducting power of the

substances employed. A vessel of lime is kept in connection with the

speculum-box to absorb the moisture, which otherwise might injure the

mirror. The process of grinding was conducted under water, and the

moving power employed was a steam-engine of three-horse power. The

Polisher is connected with the machinery by means of a large ring of

iron, which loosely encircles it; and instead of either the speculum

or the polisher being stationary, both move with a regulated speed;

the ring of the polisher, and therefore the polisher itself, has a

transverse and a longitudinal motion; it makes 80 strokes in the

minute, and 24-1/2 strokes backward and forward for every revolution

of the mirror, and at the same time 1-72/100 strokes in the transverse

direction. The extent of the latter is 27/100 of the diameter of the

speculum. The substance made use of to wear down the surface was emery

and water, a constant supply of these was kept between the grinder

and the speculum. The Grinder is made of cast iron, with grooves

cut lengthways, across and circularly on its face. The polisher and

speculum have a mutual action upon each other; in a few hours, by the

help of the emery and water, they are both ground truly circular,

whatever may have been their previous defects. The grinding is

continued till the required form of surface is produced; and this is

ascertained in the following manner. There is a high tower over the

house in which the speculum is ground, on the top of which is fixed a

pole, to which is attached the dial of a watch; there are trap doors

which open, and by means of a temporary eye-piece, allow the figure

of the dial to be seen in the speculum brought to a slight polish. If

the dots on the dial are not sufficiently well-defined, the grinding

is continued; but if they appear satisfactorily, the polishing is

commenced. It required six weeks to grind it to a fair surface. The

polisher was cut into grooves, to prevent the abraded matter from

accumulating in some places more than in others--a thin layer of pitch

was spread over it, it was smeared over with rouge and water, and a

supply of it kept up till the machinery brought it to a fine black

polish. The length of time employed for polishing the 3 feet speculum

was six hours.[48]

This large telescope is now completed, or nearly so. The tube is 56

feet long, including the speculum box, and is made of deal, one inch

thick, hooped with iron. On the inside, at intervals of 8 feet, there

are rings of iron 3 inches in depth and 1 inch broad, for the purpose

of strengthening the sides. The diameter of the tube is 7 feet. It is

fixed to mason-work, in the ground, to a large universal hinge which

allows it to turn in all directions. At 12 feet distance, on each side,

a wall is built, 72 feet long, 48 high on the outer side, and 56 on

the inner--the walls being 24 feet distant from each other, and lying

exactly in the meridional line. When directed to the south, the tube

may be lowered till it become almost horizontal; but when pointed to

the north, it only falls till it is parallel with the earth’s axis,

pointing then to the pole of the heavens. Its lateral movements take

place only from wall to wall, and this commands a view for half an hour

on each side of the meridian--that is, the whole of its motion from

east to west is limited to 15 degrees. At present it is fitted up in a

temporary way to be used as a Transit instrument; but it is ultimately

intended to connect with the tube-end galleries, machinery which shall

give an automaton movement, so that the telescope shall be used as an

Equatorial Instrument. All the works connected with this instrument

are of the strongest and safest kind; all the iron-work was cast in

his Lordship’s laboratory by men instructed by himself, and every part

of the machinery was made under his own eye, by the artizans in his

own neighbourhood, and not a single accident worth mentioning happened

during the whole proceeding.

The expence incurred by his Lordship in the erection of this noble

instrument was not less than _twelve thousand pounds_! besides the

money expended in the construction of the telescope of three feet

diameter. Sufficient time has not yet been afforded for making

particular observations with this telescope; but from slight trials

which have been made, even under unfavourable circumstances, it

promises important results. Its great superiority over every telescope

previously constructed consists in the great quantity of light it

reflects, and the brilliancy with which it exhibits objects even when

high powers are applied. It has a reflecting surface of 4,071 square

inches, while that of Herschel’s 40-feet telescope had only 1811 square

inches on its polished surface, so that the quantity of light reflected

from the speculum is considerably more than double that of Herschel’s

largest reflector. This instrument has already exceeded his Lordship’s

expectations. Many appearances before invisible in the Moon, have been

perceived, and there is every reason to expect that new discoveries

will be made by it in the _Nebulæ_, double and triple stars, and other

celestial objects. The following is an extract of a communication

from Sir James South, on this subject, addressed to the Editor of the

‘_Times_.’ ‘The leviathan telescope on which the Earl of Rosse has

been toiling upwards of two years, although not absolutely finished,

was on Wednesday last directed to the Sidereal Heavens. The letter

which I have this morning received from its noble maker, in his usual

unassuming stile, merely states, that the metal only just polished,

was of a pretty good figure, and that with a power of 500, the nebula

known as No. 2., of Messier’s catalogue, was even more magnificent than

the nebula, No. 13 of Messier, when seen with his Lordship’s telescope

of 3 feet diameter, and 27 feet focus. Cloudy weather prevented him

from turning the leviathan on any other nebulous object. Thus, then,

we have all danger of the metal breaking before it could be polished,

overcome. Little more, however, will be done with it for some time, as

the Earl is on the eve of quitting Ireland for England to resign his

post at York as President of the British Association. I look forward

with intense anxiety to witness its first severe trial, when all its

various appointments shall be completed, in the confidence that those

who may then be present, will see with it what man has never seen

before. The diameter of the large metal is 6-feet, and its focus 54

feet; yet the immense mass is manageable by one man. Compared with

it, the working telescopes of Sir William Herschel, which in his

hands conferred on astronomy such inestimable service, and on himself

astronomical immortality, were but playthings.’

The following is a more recent account of observations made by this

telescope, chiefly extracted from Sir James South’s description of

this telescope, inserted in the _Times_ of April 16th, 1845, and the

‘_Illustrated London News_’ of April 19.

‘The night of the 5th of March, 1845, was the finest I ever saw in

Ireland. Many nebulæ were observed by Lord Rosse, Dr. Robinson and

myself. Most of them were for the first time since their creation,

seen by us as groups or clusters of stars; while some, at least to

my eyes, showed no such resolution. Never, however, in my life did

I see such glorious sidereal pictures as this instrument afforded

us. Most of the nebulæ we saw I certainly have observed with my own

large achromatic; but although that instrument, as far as relates to

magnifying power, is probably inferior to no one in existence, yet to

compare these nebulæ, as seen with it and the 6-feet telescope, is like

comparing, as seen with the naked eye, the dinginess of the planet

Saturn to the brilliancy of Venus. The most popularly-known nebulæ

observed this night were the ring nebulæ in the _Canes Venatici_, or

the 51st of Messier’s catalogue, which was resolved into stars with a

magnifying power of 548, and the 94th of Messier, which is in the same

constellation, and which was resolved into a large globular cluster of

stars, not much unlike the well-known cluster in Hercules, called also

13th Messier.’ Perfection of figure, however, of a telescope, must be

tested, not by nebulæ, but by its performance on a star of the first

magnitude. If it will, under high power, show the star round and free

from optical appendages, we may safely take it for granted it will not

only show nebulæ well, but any other celestial object as it ought.

To determine this point, the telescope was directed to _Regulus_,

with the entire aperture, and a power of 800, and ‘I saw’ says Sir

James, ‘with inexpressible delight, the star free from wings, tails or

optical appendages; not indeed like a planetary disk, as in my large

achromatic, but as a round image resembling voltaic light between

charcoal points; and so little aberration had this brilliant image,

that I could have measured its distance from, and position with any of

the stars in the field with a spider’s line micrometer, and a power of

1,000, without the slightest difficulty; for, not only was the large

star round, but the telescope, although in the open air, and the wind

blowing rather fresh, was as steady as a rock.’

‘On subsequent nights, observations of other nebulæ, amounting to some

30 or more, removed most of them from the list of nebulæ, where they

had long figured, to that of clusters; while some of these latter, more

especially 5 Messier, exhibited a sidereal picture in the telescope

such as man before had never seen, and which for its magnificence

baffles all description. Several double stars were seen with various

apertures of the telescope, and with powers between 360 and 800; and

as the Earl had told us before we should,--before the speculum was

inserted in the tube, in consequence of his having been obliged to quit

the superintendence of the polishing at the most critical part of the

process,--we found that a ring of about 6 inches broad, reckoning from

the circumference of the speculum, was not perfectly polished, and to

_that_ the little irradiation seen about Regulus was unquestionably

referable. The only double stars of the 1st class which the weather

permitted us to examine with it were Xi Ursæ Majoris, and Gamma

Virginis, which I could have measured with the greatest confidence.

D’Arrest’s comet we observed on the 12th of March, with a power of

400, but nothing worthy of notice was detected. Of the Moon, a few

words must suffice. Its appearance in my large achromatic of 12 inches

aperture is known to hundreds of readers; let them then imagine that

with it they look _at_ the moon, whilst with Lord Rosse’s 6 feet they

look _into it_, and they will not form a very erroneous opinion of

the performance of the Leviathan. On the 15th of March, when the moon

was 7 days old, I never saw her unilluminated disk so beautifully,

nor her mountains so temptingly measurable. On my first looking into

the telescope, a star of about the 7th magnitude was some minutes of

a degree from the moon’s dark limb, and its occultation by the moon

appeared inevitable. The star, however, instead of disappearing the

moment the moon’s edge came in contact with it, apparently glided on

the moon’s dark face, as if it had been seen through a transparent

moon, or as if the star were between me and the moon. It remained on

the moon’s disk nearly two seconds of time, and then disappeared. I

have seen this apparent projection of a star on the moon’s face several

times, but from the great brilliancy of the star, this was the most

beautiful I ever saw. The cause of this phenomenon is involved in

impenetrable mystery.’

The following is a representation of the Great Rosse Telescope, along

with part of the buildings with which it is connected. In the interior

face of the eastern wall a very strong iron arc of about 43 feet radius

is firmly fixed, provided with adjustments, whereby its surface facing

the telescope may be set very accurately in the plane of the meridian.

On this bar, lines are drawn, the interval between any adjoining two of

which, corresponds to one minute of time on the Equator. The tube and

speculum, including the bed on which the speculum rests, weigh about

15 tons. The telescope rests on an universal joint placed on masonry

about 6 feet below the ground, and is elevated or depressed by a chain

and windlass; and although it weighs about 15 tons, the instrument is

raised by two men with great facility. Of course, it is counterpoised

in every direction. The observer when at work, stands in one of four

galleries, the three highest of which are drawn out from the western

wall, while the fourth or lowest has for its base an elevating

platform, along the horizontal surface of which a gallery slides from

wall to wall by a machinery within the observer’s reach, but which

a child may work. When the telescope is about half an hour east of

the meridian, the galleries, hanging over the gap between the walls,

present to a spectator below an appearance somewhat dangerous; yet the

observer, with common prudence, is as safe as on the ground, and each

of the galleries can be drawn from the wall to the telescope’s side so

readily, that the observer needs no one else to move it for him.

[Illustration: _figure 98._]

The above figure represents only the upper part of the tube of the

telescope, at which the observer stands when making his observations.

The telescope is at present of the Newtonian construction, and

consequently, the observer looks into the side of the tube at the upper

end of the telescope, but it is proposed to throw aside the plane

speculum, and to adapt it to the _Front view_, on the plan already

described (see pp. 306, 313, &c.) so that the observer will sit or

stand with his back towards the object, and his face looking down upon

the speculum; and, in this position, he will sometimes be elevated

between 50 and 60 feet above the ground. As yet, the telescope has no

equatorial motion, but it very shortly will; and at no very distant

day, clock-work will be connected with it, when the observer will,

while observing, be almost as comfortable, as if he were reading at a

desk by his fire-side.

[Illustration: _figure 99._]

The following figure shews a section of the machinery connected with

this telescope. It exhibits a view of the inside of the eastern wall,

with all the machinery as seen in section. A is the mason-work on the

ground, B the universal joint, which allows the tube to turn in all

directions; C the speculum in its tube; D the box; E the eye-piece; F

the moveable pulley; G the fixed one; H the chain from the side of the

tube; I the chain from the beam; K the counterpoise; L the lever; M

the chain connecting it with the tube; Z the chain which passes from

the tube to the windlass over a pulley on a truss-beam which runs from

W to the same situation on the opposite wall--the pulley is not seen.

X is a railroad on which the speculum is drawn either to or from its

box; part is cut away to show the counterpoise. The dotted line _a_

represents the course of the weight R as the tube rises or falls; it

is a segment of a circle of which the chain I is the radius. The tube

is moved from wall to wall by the ratchet and wheel at R; the wheel is

turned by the handle O, and the ratchet is fixed to the circle on the

wall. The ladders in front, as shown in the preceding sketch, enable

the observer to follow the tube in its ascent to where the galleries on

the side wall commence; these side galleries are three in number, and

each can be moved from wall to wall by the observer, after the tube,

the motion of which he also accomplishes by means of the handle O.

I shall conclude the description of this wonderful instrument in the

words of Sir James South.

‘What will be the power of this telescope when it has its Le Mairean

form’ [that is, when it is fitted up with the front view] ‘it is not

easy to divine;--what nebulæ will it resolve into stars; in what nebulæ

will it not find stars;--how many satellites of Saturn will it show

us;--how many will it indicate as appertaining to Uranus;--how many

nebulæ never yet seen by mortal eye, will it present to us;--what spots

will it show us on the various planets; will it tell us what causes

the variable brightness of many of the fixed stars;--will it give us

any information as to the constitution of the planetary nebulæ;--will

it exhibit to us any satellites encircling them; will it tell us

why the satellites of Jupiter, which generally pass over Jupiter’s

face as disks nearly of white light, sometimes traverse it as black

patches;--will it add to our knowledge of the physical construction of

nebulous stars;--of that mysterious class of bodies which surround

some stars, called, for want of a better name, ‘photospheres;’--will

it show the annular nebulæ of Lyra, merely as a brilliant luminous

ring, or will it exhibit it as thousands of stars arranged in all the

symmetry of an ellipse; will it enable us to comprehend the hitherto

incomprehensible nature and origin of the light of the great nebulæ

of Orion;--will it give us, in easily appreciable quantity, the

parallax of some of the fixed stars, or will it make sensible to us

the parallax of the nebulae themselves;--finally, having presented to

us original portraits of the moon and of the sidereal heavens, such as

man has never dared even to anticipate--will it, by Daguerreotype aid,

administer to us copies founded upon truth, and enable astronomers of

future ages to compare the moon and heavens as they then may be, with

the moon and heavens as they were? Some of these questions will be

answered affirmatively, others negatively, and that, too, very shortly;

for the noble maker of the noblest instrument ever formed by man, “has

cast his bread upon the waters, and will, with God’s blessing, find it

before many days.”’

HINTS TO AMATEURS IN ASTRONOMY RESPECTING THE CONSTRUCTION OF

TELESCOPES.

As there are many among the lower ranks of the community who have a

desire to be possessed of a telescope, which will show them some of the

prominent features of celestial scenery, but who are unable to purchase

a finished instrument at the prices usually charged by Opticians, the

following hints may perhaps be acceptable to those who are possessed of

a mechanical genius.

The lenses of an Achromatic telescope may be purchased separately

from glass-grinders or Opticians, and tubes of a cheap material may

be prepared by the individual himself for receiving the glasses.

The following are the prices at which achromatic object-glasses for

astronomical telescopes are generally sold. Focal length 30 inches,

diameter 2-1/4 inches, from 2 to 3-1/2 guineas. Focal length 42 inches,

diameter 2-3/4 inches, from 5 to 8 guineas. Focal length 42 inches,

diameter 3-1/4 inches, from 12 to 20 guineas. Focal length 42 inches,

diameter 3-3/4 inches, from 25 to 30 guineas. Eye-pieces, from 10s. 6d.

to 18 shillings. The smallest of these lenses, namely that of 2-1/4

inches diameter, if truly achromatic, may be made to bear a power of

from 80 to 100 times, in clear weather, for celestial objects, which

will show Jupiter’s moons and belts, Saturn’s ring and other celestial

phenomena. The tubes may be made either of tin plates, _papier maché_,

or wood. Wood, however, is rather a clumsy article, and it is sometimes

liable to warp, yet excellent tubes have sometimes been made of it.

Perhaps the cheapest and most convenient of all tubes when properly

made, are those formed of paper. In forming these a wooden roller of

the proper diameter should be procured, and paper of a proper size,

along with book-binder’s paste. About three or four layers only of the

paper should be pasted at one time, and, when sufficiently dry, it

should be smoothed by rubbing it with a smooth stick or ruler; after

which another series of layers should be pasted on, and allowed to dry

as before, and so on till the tube has acquired a sufficient degree

of strength and firmness. In this way, I have, by means of a few old

Newspapers, and similar materials, formed tubes as strong as if they

had been made of wood. If several tubes be intended to slide into each

other, the smallest tube should be made first, and it will serve as a

roller for forming the tube into which it is to slide.

An achromatic object glass of a shorter focal distance, and a smaller

diameter than any of those stated above, may be fitted up as a useful

astronomical telescope, when a better instrument cannot be procured. In

the Pawn-broker’s shops in London, and other places, an old achromatic

telescope, with an object-glass 20 inches focal distance and about

1-1/2 inch diameter, may be purchased at a price varying from 15 to 20

shillings. By applying an astronomical eye-piece to such a lens, if

a good one, it may bear a power, for celestial objects, of 50 or 60

times. If two plano-convex glasses, 3/4 inch focal distance, be placed

with their convex sides near to each other, they will form an eye-piece

which will produce a power on such an object-glass, of above 50 times,

which will show Jupiter’s belts and satellites, Saturn’s ring, the

solar spots, and the mountains and cavities of the moon. I have an

object-glass of this description which belonged to an old telescope,

which cost me only 12 shillings, and with which I formerly made some

useful astronomical observations. It was afterwards used as the

telescope of a small Equatorial instrument, and, with it, I was enabled

to perceive stars of the first and second magnitude, and the planets

Venus, Jupiter, and Mars, in _the day-time_.

But, should such a glass be still beyond the reach of the astronomical

amateur, let him not altogether despair. He may purchase a single lens,

3 feet focal distance, for about a couple of shillings, and by applying

an eye-glass of 1 inch focus, which may be procured for a shilling, he

will obtain a power of 36 times, which is a higher power than Galileo

was able to apply to his best telescope; and consequently, with such an

instrument, he will be enabled to perceive all the celestial objects

which that celebrated astronomer first described, and which excited so

much wonder, at that period, in the learned world. But, whatever kind

of telescope may be used, it is essentially requisite that it be placed

on a firm stand in all celestial observations: and any common mechanic

can easily form such a stand at a trifling expence.

There is a certain optical illusion to which most persons are subject,

in the first use of telescopes, especially when applied to the

celestial bodies, on which it may not be improper to make a remark.

The illusion to which I allude is this--that they are apt to imagine,

the telescope does not magnify nearly so much as it really does. They

are apt to complain of the small appearance which Jupiter and Saturn,

for example, present when magnified 160 or 200 times. With such powers

they are apt to imagine, that these bodies do not appear so large as

the moon to the naked eye. Yet it can be proved that Jupiter, when

nearest the earth, viewed with such a power, appears about 5 times

the diameter of the full moon, and 25 times larger in surface. This

appears from the following calculation. Jupiter, when in opposition,

or nearest the Earth, presents a diameter of 47´´: the mean apparent

diameter of the moon is about 31´. Multiply the diameter of Jupiter by

the magnifying power, 200, the product is 9400´´ or 156´ or 2° 36´,

which, divided by 31´, the moon’s diameter, produces a quotient of 5,

showing that this planet with such a power appears five times larger in

diameter than the full moon to the naked eye, and consequently 25 times

larger in surface. Were a power of only 50 times applied to Jupiter,

when nearest the earth, that planet would appear somewhat larger than

the full moon. For 47´´ multiplied by 50 gives 2350´´ or 39´, which

is 8´ more than the diameter of the moon. Yet with such a power most

persons would imagine that the planet does not appear one third of the

size of the full moon.

The principal mode by which a person may be experimentally convinced

of the fallacy to which I allude is the following:--At a time when

Jupiter happens to be within a few degrees of the moon, let the planet

be viewed through the telescope with the one eye, and the magnified

image of the planet be brought into contact with the moon as seen with

the other eye--the one eye looking at the moon, and the other viewing

the magnified image of Jupiter through the telescope when brought into

apparent contact with the moon--then it will be perceived, that with

a magnifying power of 50 the image of Jupiter will completely cover

the moon as seen by the naked eye;--and with a power of 200--when the

moon is made to appear in the centre of the magnified image of the

planet--it will be seen that Jupiter forms a large and broad circle

around the moon, appearing at least 5 times greater than the diameter

of the moon. This experiment may be varied as follows: Suppose a person

to view the moon through a small telescope or opera-glass, magnifying

three times, he will be apt to imagine, at first sight, that she is not

in the least magnified, but rather somewhat diminished. But let him

bring the image as seen in the telescope in contact with the moon as

seen with the naked eye, and he will plainly perceive the magnifying

power, by the size of the image. It may be difficult in the first

instance to look, at the same time, at the magnified image and the real

object, but a few trials will render it easy.

THE END.

L. SEELEY PRINTER, THAMES DITTON.

ERRATA.

Page 72 line 4 for EI, read FI.

-- 103 -- 30 -- depend, read depends.

-- 135 -- 10 -- refacting, read refracting.

-- 136 -- 10 -- colour, read colours.

-- 146 -- 27 -- G, read C.

-- 146 -- 32 -- prisms, read prism.

-- 153 -- 35 -- 28_{o} 3´, read 28° 10´

-- 165 -- 32 -- some, read since.

-- 165 -- 33 dele that.

-- 166 -- 5 for these, read their.

-- 166 -- 21 -- those, read their.

-- 178 -- 32 -- variety, read vanity.

-- 187 -- 7 -- in, read an.

-- 187 -- 11 -- (p. 103.), read (p. 72.)

-- 189 -- 30 -- lens, read lenses.

-- 199 -- 31 -- punice, read pumice.

-- 216 -- 10 -- nine, read ten.

-- 236 -- 12, 13 -- “more distant from,” read “nearer to.”

-- 337 -- 27 -- 1, read 1-1/2.

FOOTNOTES:

[1] Those unfortunate individuals who have been confined in the darkest

dungeons have declared, that though on their first entrance, no object

could be perceived, perhaps for a day or two, yet, in the course

of time, as the pupils of their eyes expanded, they could readily

perceive mice, rats, and other animals that infested their cells, and

likewise the walls of their apartments; which shows that, even in

such situations, light is present, and produces a certain degree of

influence.

[2] Letters to a German Princess, vol. l. pp. 68, 69, &c.

[3] The manner in which the motion of light was discovered is explained

in the author’s work, entitled ‘Celestial Scenery,’ pp. 369-371, and

the circumstances which led to the discovery of the aberration of light

are stated and illustrated in his volume on the ‘Sidereal Heavens,’ pp.

71-74, and pp. 284-292.

[4] Nicolson’s Introduction to Natural Philosophy, vol. 1.

[5] Light of a phosphoric nature, is frequently emitted from various

putrescent animal substances which, in the ages of superstition,

served to astonish and affright the timorous. We learn from Fabricius,

an Italian, that three young men, residing at Padua, having bought a

lamb, and eaten part of it on Easter Day, 1592, several pieces of the

remainder which they kept till the following day, shone like so many

candles when they were casually viewed in the dark. The astonishment of

the whole city was excited by this phenomenon, and a part of the flesh

was sent to Fabricius, who was Professor of anatomy, to be examined by

him. He observed, that those parts which were soft to the touch and

transparent in candle-light, were the most resplendent: and also that

some pieces of kid’s flesh which had happened to have lain in contact

with them were luminous, as well as the fingers and other parts of the

bodies of those persons who touched them. Bartholin gives an account

of a similar phenomenon, which happened at Montpelier in 1641. A poor

woman had bought a piece of flesh in the market, intending to make use

of it the following day, but happening not to be able to sleep well

that night, and her bed and pantry being in the same room, she observed

so much light come from the flesh as to illuminate all the place where

it hung. We may judge of the terror and astonishment of the woman

herself, when we find that a part of this luminous flesh was carried as

a very extraordinary curiosity to Henry, Duke of Conde, the Governor of

the place, who viewed it several hours with the greatest astonishment.

The light was as if gems had been scattered over the surface, and

continued till the flesh began to putrify, when it vanished, which

it was believed to do in the form of a cross. Hence the propriety of

instructing the mass of the community in the knowledge of the facts

connected with the material system, and the physical causes of the

various phenomena of nature.

[6] Memoires de la Soc. d’Aroncil, vol. ii.

[7] By a _medium_, in optics, is meant the space in which a ray of

light moves, whether pure space, air, water, glass, diamond, or any

other transparent substance through which the rays of light can pass in

straight lines.

[8] Edinburgh Philosophical Journal for October 1819, p. 411.

[9] This mode of finding the focus of a concave lens may be varied as

follows:--let the lens be covered with paper, having two small circular

holes; and on the paper for receiving the light, describe also two

small circles, but with their centres at twice the distance from each

other of the centres of the circles. Then move the paper to and from,

till the middle of the sun’s light, coming through the holes, falls

exactly on the middle of the circles; that distance of the paper from

the lens will be the focal length required.

[10] Small glass mirrors for performing some of the experiments, and

illustrating some of the principles above alluded to,--may be made of

the flattest kind of common watch glasses, by foliating or covering

with tin leaf and quicksilver the convex surfaces of such glasses.

Their focal distances will generally be from one to two inches. Such

mirrors afford a very large and beautiful view of the eye, when held

within their focal distance of that organ. Such mirrors will also serve

the purpose of reflecting light on the objects viewed by microscopes.

Larger mirrors, of from four to eight inches diameter, may be had of

the optician at different prices varying from five to ten or fifteen

shillings.

[11] Nicholson’s Journal of Natural Philosophy, &c. 4to. series, p. 225.

[12] There can be little doubt that some of the facts ascribed, in the

western highlands of Scotland, to _second sight_, have been owing to

the unusual refraction of the atmosphere; as one of the peculiarities

attributed to those who possessed this faculty was, that they were

enabled to descry boats and snips, before they appeared in the horizon.

[13] Fraunhofer was in the highest sense of the word, an _Optician_,

an original discoverer in the most abstruse and delicate departments

of this science--a competent mathematician, an admirable mechanist,

and a man of a truly philosophical turn of mind. By his extraordinary

talents, he was soon raised from the lowest station in a manufacturing

establishment to the direction of the _optical_ department of the

business, in which he originally laboured as an ordinary workman.

He then applied the whole power of his mind to the perfection of

the achromatic telescope, the defects of which in reference to the

optical properties of the materials used--he attempted to remedy; and

by a series of admirable experiments, succeeded in giving to optical

determinations, the precision of astronomical observations, surpassing,

in this respect all who had gone before him, except perhaps, the

illustrious Newton. It was in the course of these researches, that he

was led to the important discovery of the dark lines which occur in the

solar spectrum. His achromatic telescopes are scattered over Europe,

and are the largest and best that have hitherto been constructed. He

died at Munich, at a premature age, in 1826; his death, it is said

being accelerated by the unwholesome nature of the processes employed

in his glass-house; leaving behind him a reputation rarely attained

by one so young. His Memoir “On the refractive and dispersive power

of different species of glass, in reference to the improvement of

Achromatic telescopes, and an account of the lines on the spectrum,”

will be found in the “Edinburgh Philosophical Journal,” Vol. ix. pp.

288-299, and Vol. x. pp. 26-40, for 1823-4.

[14] Philosophical Transactions. Vol. 50. p. 294.

[15] Ecclesiasticus xliii. 11, 12.

[16] It is a question which has been frequently started--Whether there

was any rainbow before the flood? Some have conceived that the rainbow

was something of a _miraculous_ production, and that it was never

seen before the flood. The equivocal sense of the word ‘set’ in our

translation, has occasioned a mistaken impression of this kind. The

Hebrew word thus translated, signifies more properly ‘I do give,’ or

‘I _appoint_.’ The whole passage in reference to this circumstance,

literally translated, runs thus;--“I appoint my bow which is in the

cloud, that it may be for a sign or token of a covenant between me and

the earth; and it shall come to pass when I bring a cloud over the

earth, and the bow shall be seen in the cloud, that I will remember my

covenant that is between me and you,” &c. As the rainbow is produced

by the immutable laws of refraction and reflection, as applied to the

rays of the sun striking on drops of falling rain, the phenomenon must

have been occasionally exhibited from the beginning of the world:

unless we suppose that there was no rain before the flood, and that the

constitution of things in the physical system was very different from

what it is now. The passage affirms no more than that the rainbow was

_then appointed_ to be a _symbol_ of the covenant between God and man,

and although it may have been frequently seen before, it would serve

the purpose of a sign equally well, as if it had been miraculously

formed for this purpose, and even better, as its frequent appearance,

according to natural laws, is a perpetual memorial to man of the divine

faithfulness and mercy.

[17] Though Borellus mentions this circumstance, yet there is some

reason to doubt the accuracy of this statement, as young Jansen appears

to have been at that period, not more than six years old; so that it

is more probable that Galileo was the first discoverer of Jupiter’s

satellites.

[18] The reader may see an engraving of this instrument in the author’s

work entitled ‘the _Improvement of Society_.’--p. 209.

[19] It is one of the properties of concave lenses to render convergent

rays less convergent, and when placed as here supposed, to render them

parallel; and it is parallel rays that produce distinct vision.

[20] The word _aperture_ as applied to object-glasses, signifies the

opening to let in the light, or that part of the object-glass which is

left uncovered. An object-glass may be 3 inches in diameter, but if one

inch of this diameter be covered, its aperture is said to be only 2

inches.

[21] An achromatic telescope is said to be in possession of Mr. Cooper,

M.P. for Sligo, which is 26 feet long, and the diameter of the object

glass 14 inches.

[22] This telescope, which was made by Dollond, with a power of 240

times, gives a beautiful view of the belts of Jupiter and the double

ring of Saturn, and with a power of 50, the stars in the milky way and

some of the nebulæ appear very numerous and brilliant. Its owner is a

gentleman who unites science with Christianity.

[23] For a more particular account of Dr. Blair’s instruments and

experiments, the reader is referred to his Dissertation on this subject

in Vol. II. of the ‘Transactions of the Royal Society of Edinburgh,’

which occupies 76 pages--or to Nicholson’s ‘Journal of Natural

Philosophy,’ &c. Quarto Series, Vol. I., April, September, 1797.

[24] A more detailed account of the processes connected with the

construction of this telescope, will be found in a paper presented

to the Royal Society, in 1827, and published in the Philosophical

Transactions of that Society, for 1828, and likewise another paper,

published in the Transactions for 1829. From these documents, chiefly,

the preceding account has been abridged. See also the ‘Edinburgh

New Philosophical Journal’ for Jan.,--April, 1828, and Brewster’s

‘Edinburgh Journal of Science,’ for October, 1829.

[25] A particular description of this telescope, with the machinery

for moving it, illustrated with an engraving, may be seen in Reid and

Gray’s ‘Abridgement of the Philosophical Transactions.’--Vol. vi. Part

I. for 1723, pp. 147-152.

[26] Miss Short, who has erected and who superintends an observatory

on the Calton hill, Edinburgh, is the descendant of a brother of Mr.

Short. She is in possession of a large Gregorian reflector, about 12

feet long, made by Mr. Short, and mounted on an Equatorial axis. It was

originally placed in a small observatory erected on the Calton hill,

about the year 1776, but for many years past it has been little used.

[27] A particular account of the Earl of Rosse’s fifty-feet Reflector,

which is now finished, is given in the _Appendix_.

[28] Philosophical Transactions for 1800, Vol. XC. p. 80, &c.

[29] In using telescopes within doors, care should generally be taken,

that there be no fires in the apartment where they are placed for

observation, and that the air within be nearly of the same temperature

as the air of the surrounding atmosphere; for if the room be filled

with heated air, when the windows are opened, there will be a current

of cold air rushing in, and of heated air rushing out, which will

produce such an undulation and tremulous motion, as will prevent any

celestial object from being distinctly seen.

[30] The above directions and remarks are abridged with some

alterations from Dr. Pearson’s “Introduction to Practical

Astronomy.”--Vol. II.

[31] Pearson’s “Practical Astronomy.”--Vol. II.

[32] The mother-of-pearl dynameter may be purchased for about twelve

shillings. See fig. 57, _a_, _b_, _c_, p. 260.

[33] Reid’s Enquiry into the Human Mind, chap. iv.

[34] The distance of Saturn from the sun is 906,000,000 of miles; it

is sometimes nearer to and at other times farther from the earth,

according as it is near the point of its opposition to, or conjunction

with the sun. If this number be divided by 200, the supposed magnifying

power of the telescope, the quotient is 4,530,000, which expresses

the distance in miles at which it enables us to contemplate this

planet. If this number be subtracted from 906,000,000, the remainder

is 901,470,000, which expresses the number of miles from the earth at

which we are supposed to view Saturn with such an instrument.

[35] _Irish Transactions_, Vol. X. and Nicholson’s Philosophical

Journal, Vol. XVI.

[36] Brewster’s Appendix to ‘Ferguson’s Lectures.’

[37] A particular description of the micrometers here enumerated,

and several others, will be found in Dr. Pearson’s ‘Introduction to

Practical Astronomy,’ Vol. II.

[38] Adams’ Introduction to Practical Astronomy.

[39] Or find the sun’s right ascension for the given day; substract

this from the star or planet’s right ascension, and the remainder

is the approximate time of the star’s coming to the meridian. The

difference between this time and the time of observation, will then

determine the point to which the telescope is to be directed.

[40] The right ascensions, declinations, longitudes, &c., stated in

these memoranda--which were noted at the time of observation--are only

approximations to the truth; perfect accuracy in these respects being

of no importance in such observations. They are, however, in general,

within a minute or two of the truth. The _times_ of the observations,

too, are noted in reference--not to the _astronomical_, but to the

_civil_ day. The astronomical day commences at 12 noon, and the hours

are reckoned, without interruption, to the following noon. The civil

day commences at 12 midnight.

[41] This observation is inserted in the ‘Edinburgh Philosophical

Journal’ for January, 1844.

[42] The late Mr. Benjamin Martin, when describing the nature of the

solar telescope, in his ‘_Philosophia Britannica_,’ Vol. iii. p. 85,

gives the following relation:--‘I cannot here omit to mention a very

_unusual phenomenon_ that I observed about ten years ago in my darkened

room. The window looked towards the west, and the spire of Chichester

Cathedral was before it at the distance of 50 or 60 yards. I used very

often to divert myself by observing the pleasant manner in which the

sun passed behind the spire, and was eclipsed by it for sometime; for

the image of the sun and of the spire were very large, being made by a

lens of 12 feet focal distance. And once as I observed the occultation

of the sun behind the spire, just as the disk disappeared, I saw

several small, bright, round bodies or balls running toward the sun

from the dark part of the room, even to the distance of 20 inches.

I observed their motion was a little irregular, but rectilinear,

and seemed accelerated as they approached the sun. These luminous

globules appeared also on the other side of the spire, and preceded

the sun, running out into the dark room, sometimes more, sometimes

less, together in the same manner as they followed the sun at its

occultation. They appeared to be in general one-twentieth of an inch

in diameter, and therefore, must be very large luminous globes in some

part of the heavens, whose light was extinguished by that of the sun,

so that they appeared not in open day light; but whether of the meteor

kind, or what sort of bodies they might be, I could not conjecture.’

Professor Hansteen mentions, that when employed in measuring the zenith

distances of the pole star, he observed a somewhat similar phenomenon,

which he described as ‘a luminous body which passed over the field of

the universal telescope--that its motion was neither perfectly equal

nor rectilinear, but resembled very much the unequal and somewhat

serpentine motion of an ascending rocket;’ and he concluded that it

must have been ‘a meteor’ or ‘shooting star’ descending from the higher

regions of the atmosphere.[43]

In my frequent observations on Venus, to determine the nearest

positions to the sun in which that planet could be seen, I had several

times an opportunity of witnessing similar phenomena. I was not a

little surprised, when searching for the planet, frequently to perceive

a body pass across the field of the telescope, apparently of the same

size as Venus, though sometimes larger and sometimes smaller, so that

I frequently mistook that body for the planet, till its rapid motion

undeceived me. In several instances _four_ or _five_ of these bodies

appeared to cross the field of view, sometimes in a perpendicular, and,

at other times in a horizontal direction. They appeared to be luminous

bodies, somewhat resembling the appearance of a planet when viewed in

the day-time with a moderate magnifying power. Their motion was nearly

rectilinear, but sometimes inclined to a waving or serpentine form, and

they appeared to move with considerable rapidity--the telescope being

furnished with a power of about 70 times. I was for a considerable

time at a loss what opinion to form of the nature of these bodies;

but having occasion to continue these observations almost every clear

day for nearly a twelvemonth, I had frequent opportunities of viewing

this phenomenon in different aspects; and was at length enabled to

form an opinion as to the cause of at least _some_ of the appearances

which presented themselves. In several instances, the bodies alluded

to appeared much larger than usual, and to move with a more rapid

velocity; in which case I could plainly perceive that they were nothing

else than _birds_ of different sizes, and apparently at different

distances, the convex surfaces of whose bodies, in certain positions,

strongly reflected the solar rays. In other instances, when they

appeared smaller, their true shape was undistinguishable by reason of

their motion and their distance.

Having inserted a few remarks on this subject, in No. XXV. of the

Edinburgh Philosophical Journal for July, 1825, particularly in

reference to Professor Hansteen’s opinion, that article came under the

review of M. Serres, Sub-Prefect of Embrun, in a paper inserted in the

_Annales de Chemie_, for October, 1825, entitled, ‘Notices regarding

fiery meteors seen during the day.’[44] In the discussion of this

subject, M. Serres admits that the light reflected very obliquely from

the feathers of a bird is capable of producing an effect similar to

that which I have now described; but that ‘the explanation ought not

to be _generalized_.’ He remarks, that, while observing the sun at the

repeating circle, he frequently perceived, even through the coloured

glass adapted to the eye-piece, large luminous points which traversed

the field of the telescope, and which appeared too well defined not to

admit them to be distant, and subtended too large angles to imagine

them birds. In illustration of this subject he states the following

facts. On the 7th September, 1820, after having observed for some time

the eclipse of the sun which happened on that day, he intended to take

a walk in the fields, and on crossing the town, he saw a numerous group

of individuals of every age and sex, who had their eyes fixed in the

direction of the sun. Further on, he perceived another group having

their eyes in like manner turned towards the sun. He questioned an

intelligent artist who was among them to learn the object that fixed

his attention. He replied, ‘We are looking at the stars which are

detaching themselves from the sun.’ ‘You may look yourself; that will

be the shortest way to learn the fact.’ He looked, and saw, in fact,

not stars, but balls of fire of a diameter equal to the largest stars,

which were projected in various directions from the upper hemisphere

of the sun, with an incalculable velocity, and although this velocity

of projection appeared the same in all, yet they did not all attain

the same distance. These globes were projected at unequal and pretty

short intervals. Several were often projected at once, but always

diverging from one another. Some of them described a right line, and

were extinguished in the distance; some described a parabolic line, and

were in like manner extinguished; others again, after having removed

to a certain distance in a right line, retrograded upon the same line,

and seemed to enter, still luminous, into the sun’s disk. The ground of

this magnificent picture was a sky blue, somewhat tinged with brown.

Such was his astonishment at the sight of so majestic a spectacle, that

it was impossible for him to keep his eyes off it till it ceased, which

happened gradually as the eclipse wore off and the solar rays resumed

their ordinary lustre. It was remarked by one of the crowd that ‘the

sun projected most stars at the time when it was palest;’ and that the

circumstance which first excited attention to this phenomenon was that

of a woman who cried out ‘Come here!--come and see the flames that are

issuing from the sun!’

I have stated the above facts because they may afterwards tend to throw

light upon certain objects or phenomena with which we are at present

unacquainted. The phenomenon of ‘falling stars’ has of late years

excited considerable attention, and it seems now to be admitted, that,

at least, certain species of these bodies descend from regions far

beyond the limits of our atmosphere. This may be pronounced as certain

with regard to the ‘November Meteors.’ May not some of the phenomena

described above, be connected with the fall of meteoric stones--the

showers of falling stars seen on the 12th and 13th of November, or

other meteoric phenomena whose causes we have hitherto been unable to

explain? Or, may we conceive that certain celestial bodies, with whose

nature and destination we are as yet unacquainted, may be revolving in

different courses in the regions around us--some of them opaque and

others luminous, and whose light is undistinguishable by reason of the

solar effulgence?

[43] See Edinburgh Philosophical Journal, for April, 1825. No. XXIV.

[44] See Edinburgh Philosophical Journal, for July, 1826, p. 114.

[45] For an explanation of the manner of viewing Venus at her superior

conjunction, see ‘Celestial Scenery,’ 5th thousand, p. 102.

[46] See Long’s Astronomy, vol. 2, p. 487,--and Encyclopedia

Britannica, vol. ii. p. 436, 3rd edition.

[47] The balls which represent the different planets, on this machine,

have their hemispheres painted black, with the white side turned

directly to the sun, so that if the eye be placed in a line with the

earth, and the planet, particularly Mercury and Venus, its phase in the

heavens, at that time, as viewed with a telescope, may be distinctly

perceived.

[48] The above description has been selected and abridged from a small

volume entitled ‘The Monster Telescope, erected by the Earl of Rosse,

Parsontown,’--and also from the ‘Illustrated London News’ of September

9th, 1843. In the volume alluded to a more particular description will

be found, accompanied with engravings.

[Transcriber’s Note:

The corrections listed in the Errata list have been made.

The high resolution image for the image on page 196 does not have a

caption. I have captioned this image as "figure 40" and the one on page

206 as "figure 40*" to comply with the "List of Engravings".

Inconsistent double quotes and capitalization are as in the original.

Inconsistent spelling and hyphenation are as in the original.]