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[Illustration: For Description see Page 152 Frontispiece
THE GREAT NEBULA OF ORION
From a photograph taken on February 4th, 1889 by Mr Isaac Roberts.]
THROUGH MAGIC GLASSES AND OTHER LECTURES
A Sequel to The Fairyland of Science
by
ARABELLA B. BUCKLEY
(Mrs. Fisher)
Author of Life and Her Children, Winners in Life's Race,
A Short History of Natural Science, Etc.
With Numerous Illustrations
New York
D. Appleton and Company
1890
Authorized Edition.
PREFACE.
The present volume is chiefly intended for those of my young friends who
have read, and been interested in, the _Fairyland of Science_. It
travels over a wide field, pointing out a few of the marvellous facts
which can be studied and enjoyed by the help of optical instruments. It
will be seen at a glance that any one of the subjects dealt with might
be made the study of a lifetime, and that the little information given
in each lecture is only enough to make the reader long for more.
In these days, when moderate-priced instruments and good books and
lectures are so easily accessible, I hope some eager minds may be thus
led to take up one of the branches of science opened out to us by magic
glasses; while those who go no further will at least understand
something of the hitherto unseen world which is now being studied by
their help.
The two last lectures wander away from this path, and yet form a natural
conclusion to the Magician's lectures to his young Devonshire lads. They
have been published before, one in the _Youth's Companion_ of Boston,
U.S., and the other in _Atalanta_, in which the essay on Fungi also
appeared in a shorter form. All three lectures have, however, been
revised and fully illustrated, and I trust that the volume, as a whole,
may prove a pleasant Christmas companion.
For the magnificent photograph of Orion's nebula, forming the
Frontispiece, I am indebted to the courtesy of Mr. Isaac Roberts,
F.R.A.S., who most kindly lent me the plate for reproduction; and I have
had the great good fortune to obtain permission from MM. Henri of the
Paris Observatory to copy the illustration of the Lunar Apennines from a
most beautiful and perfect photograph of part of the moon, taken by them
only last March. My cordial thanks are also due to Mr. A. Cottam,
F.R.A.S., for preparing the plate of coloured double stars, and to my
friend Mr. Knobel, Hon. Sec. of the R.A.S., for much valuable
assistance; to Mr. James Geikie for the loan of some illustrations from
his _Geology_; and to Messrs. Longman for permission to copy Herschel's
fine drawing of Copernicus.
With the exception of these illustrations and a few others, three of
which were kindly given me by Messrs. Macmillan, all the woodcuts have
been drawn and executed under the superintendence of Mr. Carreras, jun.,
who has made my task easier by the skill and patience he has exercised
under the difficulties incidental to receiving instructions from a
distance.
ARABELLA B. BUCKLEY.
UPCOTT AVENEL, _Oct. 1890_.
TABLE OF CONTENTS
CHAPTER I PAGE
THE MAGICIAN'S CHAMBER BY MOONLIGHT 1
CHAPTER II
MAGIC GLASSES AND HOW TO USE THEM 27
CHAPTER III
FAIRY RINGS AND HOW THEY ARE MADE 55
CHAPTER IV
THE LIFE-HISTORY OF LICHENS AND MOSSES 75
CHAPTER V
THE HISTORY OF A LAVA STREAM 96
CHAPTER VI
AN HOUR WITH THE SUN 117
CHAPTER VII
AN EVENING AMONG THE STARS 145
CHAPTER VIII
LITTLE BEINGS FROM A MINIATURE OCEAN 172
CHAPTER IX
THE DARTMOOR PONIES 195
CHAPTER X
THE MAGICIAN'S DREAM OF ANCIENT DAYS 209
LIST OF ILLUSTRATIONS
PLATES
PHOTOGRAPH OF THE NEBULA OF ORION _Frontispiece_
TABLE OF COLOURED SPECTRA Plate I. _facing p._ 127
COLOURED DOUBLE STARS Plate II. _facing p._ 167
WOODCUTS IN THE TEXT PAGE
PARTIAL ECLIPSE OF THE MOON _Initial letter_ 1
A BOY ILLUSTRATING THE PHASES OF THE MOON 6
COURSE OF THE MOON IN THE HEAVENS 8
CHART OF THE MOON 10
FACE OF THE FULL MOON 11
TYCHO AND HIS SURROUNDINGS (from a photograph by De la Rue) 13
PLAN OF THE PEAK OF TENERIFFE 15
THE CRATER COPERNICUS 17
THE LUNAR APPENNINES (from a photograph by M.M. Henri) 19
THE CRATER PLATO SEEN SOON AFTER SUNRISE 20
DIAGRAM OF TOTAL ECLIPSE OF THE MOON 23
BOY AND MICROSCOPE _Initial letter_ 27
EYE-BALL SEEN FROM THE FRONT 30
SECTION OF AN EYE LOOKING AT A PENCIL 31
IMAGE OF A CANDLE-FLAME THROWN ON PAPER BY A LENS 33
ARROW MAGNIFIED BY A CONVEX LENS 35
STUDENT'S MICROSCOPE 36
SKELETON OF A MICROSCOPE 37
FOSSIL DIATOMS SEEN UNDER THE MICROSCOPE 39
AN ASTRONOMICAL TELESCOPE 41
TWO SKELETONS OF TELESCOPES 44
THE PHOTOGRAPHIC CAMERA 47
KIRCHHOFF'S SPECTROSCOPE 51
PASSAGE OF RAYS THROUGH THE SPECTROSCOPE 52
A GROUP OF FAIRY-RING MUSHROOMS _Initial letter_ 55
THREE FORMS OF VEGETABLE MOULD MAGNIFIED 61
_MUCOR MUCEDO_ GREATLY MAGNIFIED 63
YEAST CELLS GROWING UNDER THE MICROSCOPE 65
EARLY STAGES OF THE MUSHROOM 67
LATER STAGES OF THE MUSHROOM 68
MICROSCOPIC STRUCTURE OF MUSHROOM GILLS 69
A GROUP OF CUP LICHENS _Initial letter_ 75
EXAMPLES OF LICHENS FROM LIFE 77
SINGE-CELLED PLANTS GROWING 78
SECTIONS OF LICHENS 81
FRUCTIFICATION OF A LICHEN 83
A STEM OF FEATHERY MOSS FROM LIFE 85
MOSS-LEAF MAGNIFIED 87
_POLYTRICHUM COMMUNE_, A LARGE HAIR-MOSS 88
FRUCTIFICATION OF A MOSS 89
SPHAGNUM MOSS FROM A DEVONSHIRE BOG 93
SURFACE OF A LAVA-FLOW _Initial letter_ 96
VESUVIUS AS SEEN IN ERUPTION 97
TOP OF VESUVIUS IN 1864 100
DIAGRAMMATIC SECTION OF AN ACTIVE VOLCANO 105
SECTION OF A LAVA-FLOW 108
VOLCANIC GLASS WITH CRYSTALLITES AND MICROLITHS 109
VOLCANIC GLASS WITH WELL-DEVELOPED MICROLITHS 110
A PIECE OF DARTMOOR GRANITE 112
VOLCANIC GLASS SHOWING LARGE INCLUDED CRYSTALS 115
A TOTAL ECLIPSE OF THE SUN _Initial letter_ 117
FACE OF THE SUN PROJECTED ON A PIECE OF CARDBOARD 120
PHOTOGRAPH OF THE SUN'S FACE, taken by Mr. Selwyn
(Secchi, _Le Soleil_) 122
TOTAL ECLIPSE OF THE SUN, SHOWING CORONA AND PROMINENCES
(Guillemin, _Le Ciel_) 124
KIRCHHOFF'S EXPERIMENT ON THE DARK SODIUM LINE 128
THE SPECTROSCOPE ATTACHED TO THE TELESCOPE FOR SOLAR WORK 132
SUN-SPECTRUM AND PROMINENCE SPECTRUM COMPARED 134
RED PROMINENCES, as drawn by Mr. Lockyer 1869 136
A QUIET SUN-SPOT 140
A TUMULTUOUS SUN-SPOT 141
A STAR-CLUSTER _Initial letter_ 145
SOME CONSTELLATIONS SEEN ON LOOKING SOUTH IN MARCH FROM
SIX TO NINE O'CLOCK 148
THE CHIEF STARS OF ORION, WITH ALDEBARAN 149
THE TRAPEZIUM [Greek: th] ORIONIS 150
SPECTRUM OF ORION'S NEBULA AND SUN-SPECTRUM COMPARED 151
SOME CONSTELLATIONS SEEN ON LOOKING NORTH IN MARCH FROM
SIX TO NINE O'CLOCK 156
THE GREAT BEAR, SHOWING POSITION OF THE BINARY STAR 157
DRIFTING OF THE SEVEN STARS OF CHARLES'S WAIN 159
CASSIOPEIA AND THE HEAVENLY BODIES NEAR 162
[Greek: e] LYRAE, A DOUBLE-BINARY STAR 166
A SEASIDE POOL _Initial letter_ 172
A GROUP OF SEAWEEDS (natural size) 175
_ULVA LACTUCA_, a piece greatly magnified 176
SEAWEEDS, magnified to show fruits 177
A CORALLINE AND SERTULARIAN COMPARED 179
_SERTULARIA TENELLA_ HANGING IN WATER 180
_THURICOLLA FOLLICULATA_ AND _CHILOMONAS AMYGDALUM_ 182
A GROUP OF LIVING DIATOMS 184
A DIATOM GROWING 185
_CYDIPPE PILEUS_, ANIMAL AND STRUCTURE 187
THE SEA-MAT, _FLUSTRA FOLIACEA_ 191
DIAGRAM OF THE FLUSTRA ANIMAL 192
DARTMOOR PONIES _Initial letter_ 195
_EQUUS HEMIONUS_, THE HORSE-ASS OF TARTARY AND TIBET 201
PRZEVALSKY'S WILD HORSE 202
SKELETON OF AN ANIMAL OF THE HORSE-TRIBE 206
PALAEOLITHIC MAN CHIPPING FLINT TOOLS _Initial letter_ 209
SCENE IN PALAEOLITHIC TIMES 212
PALAEOLITHIC RELICS--NEEDLE, TOOTH, IMPLEMENT 213
MAMMOTH ENGRAVED ON IVORY 216
NEOLITHIC IMPLEMENTS--HATCHET, CELT, SPINDLE WHORL 219
A BURIAL IN NEOLITHIC TIMES 221
BRITISH RELICS--COIN, BRONZE CELT, AND BRACELET 223
BRITONS TAKING REFUGE IN THE CAVE 224
THROUGH MAGIC GLASSES
CHAPTER I
THE MAGICIAN'S CHAMBER BY MOONLIGHT
[Illustration]
The full moon was shining in all its splendour one lovely August night,
as the magician sat in his turret chamber bathed in her pure white
beams, which streamed upon him through the open shutter in the wooden
dome above. It is true a faint gleam of warmer light shone from below
through the open door, for this room was but an offshoot at the top of
the building, and on looking down the turret stairs a lecture-room might
be seen below where a bright light was burning. Very little, however, of
this warm glow reached the magician, and the implements of his art
around him looked like weird gaunt skeletons as they cast their long
shadows across the floor in the moonlight.
The small observatory, for such it was, was a circular building with
four windows in the walls, and roofed with a wooden dome, so made that
it could be shifted round and round by pulling certain cords. One
section of this dome was a shutter, which now stood open, and the strip,
thus laid bare to the night, was so turned as to face that part of the
sky along which the moon was moving. In the centre of the room, with its
long tube directed towards the opening, stood the largest magic glass,
the TELESCOPE, and in the dead stillness of the night, could be heard
distinctly the tick-tick of the clockwork, which kept the instrument
pointing to the face of the moon, while the room, and all in it, was
being carried slowly and steadily onwards by the earth's rotation on its
axis. It was only a moderate-sized instrument, about six feet long,
mounted on a solid iron pillar firmly fixed to the floor and fitted with
the clockwork, the sound of which we have mentioned; yet it looked like
a giant as the pale moonlight threw its huge shadow on the wall behind
and the roof above.
Far away from this instrument in one of the windows, all of which were
now closed with shutters, another instrument was dimly visible. This was
a round iron table, with clawed feet, and upon it, fastened by screws,
were three tubes, so arranged that they all pointed towards the centre
of the table, where six glass prisms were arranged in a semicircle, each
one fixed on a small brass tripod. A strange uncanny-looking instrument
this, especially as the prisms caught the edge of the glow streaming up
the turret stair, and shot forth faint beams of coloured light on the
table below them. Yet the magician's pupils thought it still more
uncanny and mysterious when their master used it to read the alphabet of
light, and to discover by vivid lines even the faintest trace of a metal
otherwise invisible to mortal eye.
For this instrument was the SPECTROSCOPE, by which he could break up
rays of light and make them tell him from what substances they came.
Lying around it were other curious prisms mounted in metal rims and
fitted with tubes and many strange devices, not to be understood by the
uninitiated, but magical in their effect when fixed on to the telescope
and used to break up the light of distant stars and nebulae.
Compared with these mysterious glasses the PHOTOGRAPHIC CAMERA, standing
in the background, with its tall black covering cloth, like a hooded
monk, looked comparatively natural and familiar, yet it, too, had
puzzling plates and apparatus on the table near it, which could be
fitted on to the telescope, so that by their means pictures might be
taken even in the dark night, and stars, invisible with the strongest
lens, might be forced to write their own story, and leave their image on
the plate for after study.
All these instruments told of the magician's power in unveiling the
secrets of distant space and exploring realms unknown, but in another
window, now almost hidden in the shadow, stood a fourth and
highly-prized helpmate, which belonged in one sense more to our earth,
since everything examined by it had to be brought near, and lie close
under its magnifying-glass. Yet the MICROSCOPE too could carry its
master into an unseen world, hidden to mortal eye by minuteness instead
of by distance. If in the stillness of night the telescope was his most
cherished servant and familiar friend, the microscope by day opened out
to him the fairyland of nature.
As he sat on his high pedestal stool on this summer night with the
moonlight full upon him, his whole attention was centred on the
telescope, and his mind was far away from that turret-room, wandering
into the distant space brought so near to him; for he was waiting to
watch an event which brought some new interest every time it took
place--a total eclipse of the moon. To-night he looked forward to it
eagerly, for it happened that, just as the moon would pass into the
shadow of our earth, it would also cross directly in front of a star,
causing what is known as an "occultation" of the star, which would
disappear suddenly behind the rim of the dark moon, and after a short
time flash out on the other side as the satellite went on its way.
How he wished as he sat there that he could have shown this sight to all
the eager lads whom he was teaching to handle and love his magic
glasses. For this magician was not only a student himself, he was a rich
man and the Founder and Principal of a large public school for boys of
the artisan class. He had erected a well-planned and handsome building
in the midst of the open country, and received there, on terms within
the means of their parents, working-lads from all parts of England, who,
besides the usual book-learning, received a good technical education in
all its branches. And, while he left to other masters the regular
school lessons, he kept for himself the intense pleasure of opening the
minds of these lads to the wonders of God's universe around them.
You had only to pass down the turret stairs, into the large science
class-room below, to see at once that a loving hand and heart had
furnished it. Not only was there every implement necessary for
scientific work, but numerous rough diagrams covering the walls showed
that labour as well as money had been spent in decorating them. It was a
large oblong room, with four windows to the north, and four to the
south, in each of which stood a microscope with all the tubes, needles,
forceps, knives, etc., necessary for dissecting and preparing objects;
and between the windows were open shelves, on which were ranged
chemicals of various kinds, besides many strange-looking objects in
bottles, which would have amused a trained naturalist, for the lads
collected and preserved whatever took their fancy.
On some of the tables were photographic plates laid ready for printing
off; on others might be seen drawings of the spectrum, made from the
small spectroscope fixed at one end of the room; on others lay small
direct spectroscopes which the lads could use for themselves. But
nowhere was a telescope to be seen. This was not because there were
none, for each table had its small hand-telescope, cheap but good. The
truth is that each of these instruments had been spirited away into the
dormitories that night, and many heads were lying awake on their
pillows, listening for the strike of the clock to spring out and see
the eclipse begin.
[Illustration: Fig. 1.
A boy illustrating the phases of the moon.]
A mere glance round the room showed that the moon had been much studied
lately. On the black-board was drawn a rough diagram, showing how a boy
can illustrate for himself the moon's journey round the earth, by taking
a ball and holding it a little above his head at arm's length, while he
turns slowly round on his heel in a darkened room before a lighted lamp,
or better still before the lens of a magic lantern (Fig. 1). The lamp or
lens then represents the sun, the ball is the moon, the boy's head is
the earth. Beginning with the ball between him and the source of light,
but either a little above, or a little below the direct line between his
eye and it, he will see only the dark side of the ball, and the moon
will be on the point of being "new." Then as he turns slowly, a thin
crescent of light will creep over the side nearest the sun, and by
degrees encroach more and more, so that when he has turned through one
quarter of the round half the disc will be light. When he has turned
another quarter, and has his back to the sun, a full moon will face him.
Then as he turns on through the third quarter a crescent of darkness
creeps slowly over the side away from the sun, and gradually the bright
disc is eaten away by shadow till at the end of the third quarter half
the disc again only is light; then, when he has turned through another
quarter and completed the circle, he faces the light again and has a
dark moon before him. But he must take care to keep the moon a little
above or a little below his eye at new and full moon. If he brings it
exactly on a line with himself and the light at new moon, he will shut
off the light from himself and see the dark body of the ball against the
light, causing an _eclipse_ of the sun; while if he does the same at
full moon his head will cast a shadow on the ball causing an _eclipse_
of the moon.
There were other diagrams showing how and why such eclipses do really
happen at different times in the moon's path round the earth; but
perhaps the most interesting of all was one he had made to explain what
so few people understand, namely, that though the moon describes a
complete circle round our earth every month, yet she does not describe a
circle in space, but a wavy line inwards and outwards across the
earth's path round the sun. This is because the earth is moving on all
the while, carrying the moon with it, and it is only by seeing it drawn
before our eyes that we can realise how it happens.
Thus suppose, in order to make the dates as simple as possible, that
there is a new moon on the 1st of some month. Then by the 9th (or
roughly speaking in 7-3/4 days) the moon will have described a quarter
of a circle round the earth as shown by the dotted line (Fig. 2), which
marks her position night after night with regard to us. Yet because she
is carried onwards all the while by the earth, she will really have
passed along the interrupted line - - - - between us and the sun. During
the next week her quarter of a circle will carry her round behind the
earth, so that we see her on the 17th as a full moon, yet her actual
movement has been onwards along the interrupted line on the farther side
of the earth. During the third week she creeps round another quarter of
a circle so as to be in advance of the earth on its yearly journey round
the sun, and reaches the end of her third quarter on the 24th. In her
last quarter she gradually passes again between the earth and the sun;
and though, as regards the earth, she appears to be going back round to
the same place where she was at the beginning of the month, and on the
31st is again a dark new moon, yet she has travelled onwards exactly as
much as we have, and therefore has really not described a circle in the
_heavens_ but a wavy line.
[Illustration: Fig. 2.
Diagram showing the moon's course during one month. The moon and the
earth are both moving onwards in the direction of the arrows. The earth
moves along the dark line, the moon along the interrupted line - - - -.
The dotted curved line .... shows the circle gradually described by the
moon round the earth as they move onwards.]
Near to this last diagram hung another, well loved by the lads, for it
was a large map of the _face_ of the moon, that is of the side which is
_always_ turned towards us, because the moon turns once on her axis
during the month that she is travelling round the earth. On this map
were marked all the different craters, mountains, plains and shining
streaks which appear on the moon's face; while round the chart were
pictures of some of these at sunrise and sunset on the moon, or during
the long day of nearly a fortnight which each part of the face enjoys in
its turn.
[Illustration: Fig. 3.
Chart of the moon.
Craters--
1 Tycho. 4 Aristarchus. 7 Plato. 10 Petavius.
2 Copernicus. 5 Eratosthenes. 8 Eudoxus. 11 Ptolemy.
3 Kepler. 6 Archimedes. 9 Aristotle.
Grey plains formerly believed to be seas--
A Mare Crisium. O Mare Imbrium.
C ---- Frigoris. Q Oceanus Procellarum.
G ---- Tranquillitatis. X Mare Foecunditatis.
H ---- Serenitatis. T ---- Humorum.]
By studying this map, and the pictures, they were able, even in their
small telescopes, to recognise Tycho and Copernicus, and the mountains
of the moon, after they had once grown accustomed to the strange
changes in their appearance which take place as daylight or darkness
creeps over them. They could not however pick out more than some of the
chief points. Only the magician himself knew every crater and ridge
under all its varying lights, and now, as he waited for the eclipse to
begin, he turned to a lad who stood behind him, almost hidden in the
dark shadow--the one fortunate boy who had earned the right to share
this night's work.
[Illustration: Fig. 3_a_.
The full moon. (From Ball's _Starland_.)]
"We have still half an hour, Alwyn," said he, "before the eclipse will
begin, and I can show you the moon's face well to-night. Take my place
here and look at her while I point out the chief features. See first,
there are the grey plains (A, C, G, etc.) lying chiefly in the lower
half of the moon. You can often see these on a clear night with the
naked eye, but you must remember that then they appear more in the upper
part, because in the telescope we see the moon's face inverted or upside
down.
"These plains were once thought to be oceans, but are now proved to be
dry flat regions situated at different levels on the moon, and much like
what deserts and prairies would appear on our earth if seen from the
same distance. Looking through the telescope, is it not difficult to
imagine how people could ever have pictured them as a man's face? But
not so difficult to understand how some ancient nations thought the moon
was a kind of mirror, in which our earth was reflected as in a
looking-glass, with its seas and rivers, mountains and valleys; for it
does look something like a distant earth, and as the light upon it is
really reflected from the sun it was very natural to compare it to a
looking-glass.
"Next cast your eye over the hundreds of craters, some large, others
quite small, which cover the moon's face with pitted marks, like a man
with small-pox; while a few of the larger rings look like holes made in
a window-pane, where a stone has passed through, for brilliant shining
streaks radiate from them on all sides like the rays of a star, covering
a large part of the moon. Brightest of all these starred craters is
Tycho, which you will easily find near the top of the moon (I, Fig. 3),
for you have often seen it in the small telescope. How grand it looks
to-night in the full moon (Fig. 3_a_)! It is true you see all the
craters better when the moon is in her quarters, because the light falls
sideways upon them and the shadows are more sharply defined; yet even at
the full the bright ray of light on Tycho's rim marks out the huge
cavity, and you can even see faintly the magnificent terraces which run
round the cup within, one below the other."
[Illustration: Fig. 4.
Tycho and his surroundings. (From a photograph of the moon taken by Mr.
De la Rue, 1863.)]
"This cavity measures fifty-four miles across, so that if it could be
moved down to our earth it would cover by far the largest part of
Devonshire, or that portion from Bideford on the north, to the sea on
the south, and from the borders of Cornwall on the east, to Exeter on
the west, and it is 17,000 feet or nearly three miles in depth. Even in
the brilliant light of the full moon this enormous cup is dark compared
to the bright rim, but it is much better seen in about the middle of the
second quarter, when the rising sun begins to light up one side while
the other is in black night. The drawing on the wall (Fig. 4), which is
taken from an actual photograph of the moon's face, shows Tycho at this
time surrounded by the numerous other craters which cover this part of
the moon. You may recognise him by the gleaming peak in the centre of
the cup, and by his bright rim which is so much more perfect than those
of his companions. The gleaming peak is the top of a steep cone or hill
rising up 6000 feet, or more than a mile from the base of the crater, so
that even the summit is about two miles below the rim.
"There is one very interesting point in Tycho, however, which is seen at
its very best at full moon. Look outside the bright rim and you will see
that from the shadow which surrounds it there spring on all sides those
strange brilliant streaks (see Fig. 3_a_) which I spoke of just now.
There are others quite as bright, or even brighter, round other craters,
Copernicus (Fig. 6), Kepler, and Aristarchus, lower down on the
right-hand side of the moon; but these of Tycho are far the most widely
spread, covering almost all the top of the face.
"What are these streaks? We do not know. During the second quarter of
the moon, when the sun is rising slowly upon Tycho, lighting up his
peak and showing the crater beautifully divided into a bright cup in the
curve to the right, while a dense shadow lies in the left hollow, these
streaks are only faint, and among the many craters around (see Fig. 4)
you might even have some difficulty at first in finding the well-known
giant. But as the sun rises higher and higher they begin to appear, and
go on increasing in brightness till they shine with that wonderfully
silvery light you see now in the full moon."
[Illustration: Fig. 5.
Plan of the Peak of Teneriffe, showing how it resembles a lunar crater.
(A. Geikie.)]
"Here is a problem for you young astronomers to solve, as we learn more
and more how to use the telescope with all its new appliances."
The crater itself is not so difficult to explain, for we have many like
it on our earth, only not nearly so large. In fact, we might almost say
that our earthly volcanoes differ from those in the moon only by their
smaller size and by forming _mountains_ with the crater or cup on the
top; while the lunar craters lie flat on the surface of the moon, the
hollow of the cup forming a depression below it. The peak of Teneriffe
(Fig. 5), which is a dormant volcano, is a good copy in miniature on our
earth of many craters on the moon. The large plain surrounded by a high
rocky wall, broken in places by lava streams, the smaller craters
nestling in the cup, and the high peak or central crater rising up far
above the others, are so like what we see on the moon that we cannot
doubt that the same causes have been at work in both cases, even though
the space enclosed in the rocky wall of Teneriffe measures only eight
miles across, while that of Tycho measures fifty-four.
"But of the streaks we have no satisfactory explanation. They pass alike
over plain and valley and mountain, cutting even across other craters
without swerving from their course. The astronomer Nasmyth thought they
were the remains of cracks made when the volcanoes were active, and
filled with molten lava from below, as water oozes up through ice-cracks
on a pond. But this explanation is not quite satisfactory, for the lava,
forcing its way through, would cool in ridges which ought to cast a
shadow in sunlight. These streaks, however, not only cast no shadow, as
you can see at the full moon but when the sun shines sideways upon them
in the new or waning moon they disappear as we have seen altogether.
Thus the streaks, so brilliant at full moon in Tycho, Copernicus,
Kepler, and Aristarchus, remain a puzzle to astronomers still."
[Illustration: Fig. 6.
The crater Copernicus. (As given in Herschel's _Astronomy_, from a
drawing taken in a reflecting telescope of 20 feet focal length.)]
"We cannot examine these three last-named craters well to-night with the
full sun upon them; but mark their positions well, for Copernicus, at
least, you must examine on the first opportunity, when the sun is
rising upon it in the moon's second quarter. It is larger even than
Tycho, measuring fifty-six miles across, and has a hill in the centre
with many peaks; while outside, great spurs or ridges stretch in all
directions sometimes for more than a hundred miles, and between these
are scattered innumerable minute craters. But the most striking feature
in it is the ring, which is composed inside the crater of magnificent
terraces divided by deep ravines. These terraces are in some ways very
like those of the great crater of Teneriffe, and astronomers can best
account for them by supposing that this immense crater was once filled
with a lake of molten lava rising, cooling at the edges, and then
falling again, leaving the solid ridge behind. The streaks are also
beautifully shown in Copernicus (see Fig. 6), but, as in Tycho, they
fade away as the sun sets on the crater, and only reappear gradually as
midday approaches.
"And now, looking a little to the left of Copernicus, you will see that
grand range of mountains, the Lunar Apennines (Fig. 7), which stretches
400 miles across the face of the moon. Other mountain ranges we could
find, but none so like mountains on our own globe as these, with their
gentle sunny slope down to a plain on the left, and steep perpendicular
cliffs on the right. The highest peak in this range, called Huyghens,
rises to the height of 21,000 feet, higher than Chimborazo in the Andes.
Other mountains on the moon, such as those called the Caucasus, south of
the Apennines, are composed of disconnected peaks, while others again
stand as solitary pyramids upon the plains."
[Illustration: Fig. 7.
The Lunar Apennines.
(Copied by kind permission of MM. Henri from part of a magnificent
photograph taken by them, March 29, 1890, at the Paris Observatory.)]
"But we must hasten on, for I want you to observe those huge walled
crater-plains which have no hill in the middle, but smooth steel-grey
centres shining like mirrors in the moonlight. One of these, called
Archimedes, you will find just below the Lunar Apennines (Figs. 3 and
7), and another called Plato, which is sixty miles broad, is still lower
down the moon's face (Figs. 3 and 8). The centres of these broad
circles are curiously smooth and shining like quicksilver, with minute
dots here and there which are miniature craters, while the walls are
rugged and crowned with turret-shaped peaks."
[Illustration: Fig. 8.
The crater Plato as seen soon after sunrise. (After Neison.)]
"It is easy to picture to oneself how these may once have been vast seas
of lava, not surging as in Copernicus, and heaving up as it cooled into
one great central cone, but seething as molten lead does in a crucible,
little bubbles bursting here and there into minute craters; and this is
the explanation given of them by astronomers.
"And now that you have seen the curious rugged face of the moon and its
craters and mountains, you will want to know how all this has come
about. We can only form theories on the point, except that everything
shows that heat and volcanoes have in some way done the work, though no
one has ever yet clearly proved that volcanic eruptions have taken place
in our time. We must look back to ages long gone by for those mighty
volcanic eruptions which hurled out stones and ashes from the great
crater of Tycho, and formed the vast seas of lava in Copernicus and
Plato.
"And when these were over, and the globe was cooling down rapidly, so
that mountain ranges were formed by the wrinkling and rending of the
surface, was there then any life on the moon? Who can tell? Our magic
glasses can reveal what now is, so far as distance will allow; but what
has been, except where the rugged traces remain, we shall probably never
know. What we now see is a dead worn-out planet, on which we cannot
certainly trace any activity except that of heat in the past. That there
is no life there now, at any rate of the kind on our own earth, we are
almost certain; first, because we can nowhere find traces of water,
clouds, nor even mist, and without moisture no life like ours is
possible; and secondly, because even if there is, as perhaps there may
be, a thin ocean of gas round the moon there is certainly no atmosphere
such as surrounds our globe.
"One fact which proves this is, that there are no half-shadows on the
moon. If you look some night at the mountains and craters during her
first and second quarters, you will be startled to see what heavy
shadows they cast, not with faint edges dying away into light, but sharp
and hard (see Figs. 6-8), so that you pass, as it were by one step, from
shadow to sunshine. This in itself is enough to show that there is no
air to scatter the sunlight and spread it into the edges of the shade as
happens on our earth; but there are other and better proofs. One of
these is, that during an eclipse of the sun there is no reflection of
his light round the dark moon as there would be if the moon had an
atmosphere; another is that the spectroscope, that wonderful instrument
which shows us invisible gases, gives no hint of air around the moon;
and another is the sudden disappearance or _occultation_ of a star
behind the moon, such as I hope to see in a few minutes.
"See here! take the small hand telescope and turn it on to the moon's
face while I take my place at the large one, and I will tell you what to
look for. You know that at sunset we see the sun for some time after it
has dipped below the horizon, because the rays of light which come from
it are bent in our atmosphere and brought to our eyes, forming in them
the image of the sun which is already gone. Now in a short time the moon
which we are watching will be darkened by our earth coming between it
and the sun, and while it is quite dark it will pass over a little
bright star. In fact to us the star will appear to set behind the dark
moon as the sun sets below the horizon, and if the moon had an
atmosphere like ours, the rays from the star would be bent in it and
reach our eyes after the star was gone, so that it would only disappear
gradually. Astronomers have always observed, however, that the star is
lost to sight quite suddenly, showing that there is no ocean of air
round the moon to bend the light-rays."
[Illustration: Fig. 9.
Diagram of total eclipse of the moon.
S, Sun. E, Earth. M, Moon passing into the earth's shadow and passing
out at M'.
R, R', Lines meeting at a point U, U' behind the earth and enclosing a
space within which all the direct rays of the sun are intercepted by the
earth, causing a black darkness or _umbra_.
R, P and R', P', Lines marking a space within which, behind the earth,
part of the sun's rays are cut off, causing a half-shadow or _penumbra_,
P, P'.
_a_, _a_, Points where a few of the sun's rays are bent or refracted in
the earth's atmosphere, so that they pass along the path marked by the
dotted lines and shed a lurid light on the sun's face.]
Here the magician paused, for a slight dimness on the lower right-hand
side of the moon warned him that she was entering into the _penumbra_ or
half-shadow (see Fig. 9) caused by the earth cutting off part of the
sun's rays; and soon a deep black shadow creeping over Aristarchus and
Plato showed that she was passing into that darker space or _umbra_
where the body of the earth is completely between her and the sun and
cuts off all his rays. All, did I say? No! not all. For now was seen a
beautiful sight, which would prove to any one who saw our earth from a
great distance that it has a deep ocean of air round it.
It was a clear night, with a cloudless sky, and as the deep shadow crept
slowly over the moon's face, covering the Lunar Apennines and
Copernicus, and stealing gradually across the brilliant streaks of Tycho
till the crater itself was swallowed up in darkness, a strange lurid
light began to appear. The part of the moon which was eclipsed was not
wholly dark, but tinted with a very faint bluish-green light, which
changed almost imperceptibly, as the eclipse went on, to rose-red, and
then to a fiery copper-coloured glow as the moon crept entirely into the
shadow and became all dark. The lad watching through his small telescope
noted this weird light, and wondered, as he saw the outlines of the
Apennines and of several craters dimly visible by it, though the moon
was totally eclipsed. He noted, but was silent. He would not disturb the
Principal, for the important moment was at hand, as this dark
copper-coloured moon, now almost invisible, drew near to the star over
which it was to pass.
This little star, really a glorious sun billions of miles away behind
the moon, was perhaps the centre of another system of worlds as unknown
to us as we to them, and the fact of our tiny moon crossing between it
and our earth would matter as little as if a grain of sand was blown
across the heavens. Yet to the watchers it was a great matter--would the
star give any further clue to the question of an atmosphere round the
moon? Would its light linger even for a moment, like the light of the
setting sun? Nearer and nearer came the dark moon; the star shone
brilliantly against its darkness; one second and it was gone. The long
looked-for moment had passed, and the magician turned from his
instrument with a sigh. "I have learnt nothing new, Alwyn," said he,
"but at least it is satisfactory to have seen for ourselves the proof
that there is no perceptible atmosphere round the moon. We need wait no
longer, for before the star reappears on the other side the eclipse will
be passing away."
"But, master," burst forth the lad, now the silence was broken, "tell me
why did that strange light of many tints shine upon the dark moon?"
"Did you notice it, Alwyn?" said the Principal, with a pleased smile.
"Then our evening's work is not lost, for you have made a real
observation for yourself. That light was caused by the few rays of the
sun which grazed the edge of our earth passing through the ocean of air
round it (see Fig. 9). There they were refracted or bent, and so were
thrown within the shadow cast by our earth, and fell upon the moon. If
there were such a person as a 'man in the moon,' that lurid light would
prove to him that our earth has an atmosphere. The cause of the tints is
the same which gives us our sunset colours, because as the different
coloured waves which make white light are absorbed one by one, passing
through the denser atmosphere, the blue are cut off first, then the
green, then the yellow, till only the orange and red rays reached the
centre of the shadow, where the moon was darkest. But this is too
difficult a subject to begin at midnight."
So saying, he lighted his lamp, and covering the object-glass of his
telescope with its pasteboard cap, detached the instrument from the
clockwork, and the master and his pupil went down the turret stairs and
past through the room below. As they did so they heard in the distance a
scuffling noise like that of rats in the wall. A smile passed over the
face of the Principal, for he knew that his young pupils, who had been
making their observations in the gallery above, were hurrying back to
their beds.