years ago did not have an attractive air. It savored too much of
charlatanism. But it soon appeared that effective government
sanction had been given to the enterprise; and, above all,
that men of reputation were allowing the use of their names in
connection with the affair. More important still, we learned that
the actual construction had been undertaken by Gautier, of Paris,
that finances were favorable, and that real work on parts of the
instrument was to commence without delay.
Gautier is a first-class instrument-builder; he has established
his reputation by constructing successfully several telescopes of
very large size, including the _equatorial coudé_ of the Paris
Observatory, a unique instrument of especial complexity. The
present writer believes that, if sufficient time and money were
available, the _Grande Lunette_ would stand a reasonable chance of
success in the hands of such a man. And by a reasonable chance, we
mean that there is a large enough probability of genuine scientific
discovery to justify the necessary financial outlay. But the
project should be divorced from its "popular" features, and every
kind of advertising and charlatanism excluded with rigor.
As planned originally, and actually constructed, the _Grande
Lunette_ presents interesting peculiarities, distinguishing it
from other telescopes. Previous instruments have been built on the
principle of universal mobility. It is possible to move them in
all directions, and thus bring any desired star under observation,
irrespective of its position in the sky. But this general mobility
offers great difficulties in the case of large and ponderous
telescopes. Delicacy of adjustment is almost destroyed when the
object to be adjusted weighs several tons. And the excessive
weight of telescopes is not due to unavoidably heavy lenses alone.
It is essential that the tube be long; and great length involves
appreciable thickness of material, if stiffness and solidity are to
remain unsacrificed. Length in the tube is necessitated by certain
peculiar optical defects of all lenses, into the nature of which we
shall not enter at present. The consequences of these defects can
be rendered harmless only if the instrument is so arranged that the
observer's eye is far from the other end of the tube. The length
of a good telescope should be at least twelve times the diameter
of its large lens. If the relative length can be still further
increased, so much the better; for then the optical defects can be
further reduced.
In the case of the Paris instrument a radical departure consists
in making the tube of unprecedented length, 197 feet, with a
lens diameter of 49¼ inches. This great length, while favorable
optically, precludes the possibility of making the instrument
movable in the usual sense. In fact, the entire tube is attached
to a fixed horizontal base, and no attempt is made to change its
position. Outside the big lens, and disconnected altogether from
the telescope proper, is mounted a smooth mirror, so arranged that
it can be turned in any direction, and thus various parts of the
sky examined by reflection in the telescope.
While this method unquestionably has the advantage of leaving
the optician quite free as to how long he will make his tube, it
suffers from the compensating objection that a new optical surface
is introduced into the combination, viz., the mirror. Any slight
unavoidable imperfection in the polishing of its surface will
infallibly be reproduced on a magnified scale in the image of a
distant star brought before the observer's eye.
But it is not yet possible to pronounce definitely upon the merit
of this form of instrument, since, as we have said, the maker
has not been given time enough to try the idea to the complete
satisfaction of scientific men. In the early part of August, 1900,
when the informant of the present writer left Paris, after serving
as a member of the international jury for judging instruments of
precision at the Exposition, the condition of the _Grande Lunette_
was as follows: Two sets of lenses had been contemplated, one
intended for celestial photography, and the other to be used for
ordinary visual observation. Only the photographic lenses had been
completed, however, and for this reason the public could not be
permitted to look through the instrument. The photographic lenses
were in place in the tube, but at that time their condition was
such that, though some photographs had been obtained, it was
not thought advisable to submit them to the jury. Consequently,
the _Lunette_ did not receive a prize. Since that time various
newspapers have reported wonderful results from the telescope;
but, disregarding the fusillade from the sensational press, we may
sum up the present state of affairs very briefly. Gautier is still
experimenting; and, given sufficient time and money, he may succeed
in producing what astronomers hope for--an instrument capable of
advancing our knowledge, even if that advance be only a small one.
THE ASTRONOMER'S POLE
The pole of the frozen North is not the only pole sought with
determined effort by more than one generation of scientific men. Up
in the sky astronomers have another pole which they are following
up just as vigorously as ever Arctic explorer struggled toward
the difficult goal of his terrestrial journeying. The celestial
pole is, indeed, a fundamentally important thing in astronomical
science, and the determination of its exact position upon the
sky has always engaged the closest attention of astronomers.
Quite recently new methods of research have been brought to
bear, promising a degree of success not hitherto attained in the
astronomers' pursuit of their pole.
In the first place, we must explain what is meant by the celestial
pole. We have already mentioned the poles of the earth (p. 136).
Our planet turns once daily upon an axis passing through its
centre, and it is this rotation that causes all the so-called
diurnal phenomena of the heavens. Rising and setting of sun, moon,
and stars are simply results of this turning of the earth. Heavenly
bodies do not really rise; it is merely the man on the earth who is
turned round on an axis until he is brought into a position from
which he can see them. The terrestrial poles are those two points
on the earth's surface where it is pierced by the rotation axis of
the planet. Now we can, if we choose, imagine this axis lengthened
out indefinitely, further and further, until at last it reaches the
great round vault of the sky. Here it will again pierce out two
polar points; and these are the celestial poles.
The whole thing is thus quite easy to understand. On the sky the
poles are marked by the prolongation of the earth's axis, just as
on the earth the poles are marked by the axis itself. And this
explains at once why the stars seem nightly to revolve about the
pole. If the observer is being turned round the earth's axis, of
course it will appear to him as if the stars were rotating around
the same axis in the opposite direction, just as houses and fields
seem to fly past a person sitting in a railway train, unless he
stops to remember that it is really himself who is in motion, and
not the trees and houses.
The existence of such a centre of daily motions among the stars
once recognized, it becomes of interest to ascertain whether the
centre itself always retains precisely the same position in the
sky. It was discovered as early as the time of Hipparchus (p. 39)
that such is not the case, and that the celestial pole is subject
to a slow motion among the stars on the sky. If a given star were
to-day situated exactly at the pole, it would no longer be there
after the lapse of a year's time; for the pole would have moved
away from it.
This motion of the pole is called precession. It means that certain
forces are continually at work, compelling the earth's axis to
change its position, so that the prolongation of that axis must
pierce the sky at a point which moves as time goes on. These forces
are produced by the gravitational attractions of the sun, moon,
and planets upon the matter composing our earth. If the earth
were perfectly spherical in shape, the attractions of the other
heavenly bodies would not affect the direction of the earth's
rotation-axis in the least. But the earth is not quite globular in
form; it is flattened a little at the poles and bulges out somewhat
at the equator. (See p. 135.)
This protuberant matter near the equator gives the other bodies
in the solar system an opportunity to disturb the earth's
rotation. The general effect of all these attractions is to make
the celestial pole move upon the sky in a circle having a radius
of about 23½ degrees; and it requires 25,800 years to complete
a circuit of this precessional cycle. One of the most striking
consequences of this motion will be the change of the polar star.
Just at present the bright star Polaris in the constellation of
the Little Bear is very close to the pole. But after the lapse of
sufficient ages the first-magnitude star Vega of the constellation
Lyra will in its turn become Guardian of the Pole.
It must not be supposed, however, that the motion of the pole
proceeds quite uniformly, and in an exact circle; the varying
positions of the heavenly bodies whose attractions cause
the phenomena in question are such as to produce appreciable
divergencies from exact circular motion. Sometimes the pole
deviates a little to one side of the precessional circle, and
sometimes it deviates on the other side. The final result is a
sort of wavy line, half on one side and half on the other of an
average circular curve. It takes only nineteen years to complete
one of these little waves of polar motion, so that in the
whole precessional cycle of 25,800 years there are about 1,400
indentations. This disturbance of the polar motion is called by
astronomers nutation.
The first step in a study of polar motion is to devise a method of
finding just where the pole is on any given date. If the astronomer
can ascertain by observational processes just where the pole is
among the stars at any moment, and can repeat his observations year
after year and generation after generation, he will possess in
time a complete chart of a small portion at least of the celestial
pole's vast orbit. From this he can obtain necessary data for a
study of the mathematical theory of attractions, and thus, perhaps,
arrive at an explanation of the fundamental laws governing the
universe in which we live.
The instrument which has been used most extensively for the
study of these problems is the transit (p. 118) or the "meridian
circle." This latter consists of a telescope firmly attached to a
metallic axis about which it can turn. The axis itself rests on
massive stone supports, and is so placed that it points as nearly
as possible in an east-and-west direction. Consequently, when the
telescope is turned about its axis, it will trace out on the sky
a great circle (the meridian) which passes through the north and
south points of the horizon and the point directly overhead. The
instrument has also a metallic circle very firmly fastened to
the telescope and its axis. Let into the surface of this circle
is a silver disk upon which are engraved a series of lines or
graduations by means of which it is possible to measure angles.
Observers with the meridian circle begin by noting the exact
instant when any given star passes the centre of the field of
view of the telescope. This centre is marked with a cross made
by fastening into the focus some pieces of ordinary spider's web,
which give a well-marked, delicate set of lines, even under the
magnifying power of the telescope's eye-piece. In addition to thus
noting the time when the star crosses the field of the telescope,
the astronomer can measure by means of the circle, how high up it
was in the sky at the instant when it was thus observed.
If the telescope of the meridian circle be turned toward the north,
and we observe stars close to the pole, it is possible to make two
different observations of the same star. For the close polar stars
revolve in such small circles around the pole of the heavens that
we can observe them when they are on the meridian either above the
pole or below it. Double observations of this class enable us to
obtain the elevation of the pole above the horizon, and to fix its
position with respect to the stars.
Now, there is one very serious objection to this method. In order
to secure the two necessary observations of the same star, it is
essential to be stationed at the instrument at two moments of time
separated by exactly twelve hours; and if one of the observations
occurs in the night, the other corresponding observation will occur
in daylight.
It is a fact not generally known that the brighter stars can be
seen with a telescope, even when the sun is quite high above
the horizon. Unfortunately, however, there is only one star
close to the pole which is bright enough to be thus observed in
daylight--the polar star already mentioned under the name Polaris.
The fact that we are thus limited to observations of a single
star has made it difficult even for generations of astronomers
to accumulate with the meridian circle a very large quantity of
observational material suitable for the solution of our problem.
The new method of observation to which we have referred above
consists in an application of photography to the polar problem. If
we aim at the pole a powerful photographic telescope, and expose a
photographic plate throughout the entire night, we shall find that
all stars coming within the range of the plate will mark out little
circles or "trails" upon the developed negative. It is evident that
as the stars revolve about the pole on the sky, tracing out their
daily circular orbits, these same little circles must be reproduced
faithfully upon the photographic plate. The only condition is that
the stars shall be bright enough to make their light affect the
sensitive gelatine surface.
But even if observations of this kind are continued throughout
all the hours of darkness, we do not obtain complete circles,
but only those portions of circles traced out on the sky between
sunset and sunrise. If the night is twelve hours in length, we
get half-circles on the plate; if it is eighteen hours long, we
get circles that lack only one-quarter of being complete. In
other words, we get a series of circular arcs, one corresponding
to each close polar star. There are no fewer than sixteen stars
near enough to the pole to come within the range of a photographic
plate, and bright enough to cause measurable impressions upon
the sensitive surface. The fact that the circular arcs are not
complete circles does not in the least prevent our using them for
ascertaining the position of their common centre; and that centre
is the pole. Moreover, as the arcs are distributed at all sorts
of distances from the pole and in all directions, corresponding to
the accidental positions of the stars on the sky, we have a state
of affairs extremely favorable to the accurate determination of the
pole's place among the stars by means of microscopic measurements
of the plate.
It will be perceived that this method is extremely simple, and,
therefore, likely to be successful; though its simplicity is
slightly impaired by the phenomenon known to astronomers as
"atmospheric refraction." The rays of light coming down to our
telescopes from a distant star must pass through the earth's
atmosphere before they reach us; and in passing thus from the
nothingness of outer space into the denser material of the air,
they are bent out of their straight course. The phenomenon is
analogous to what we see when we push a stick down through the
surface of still water; we notice that the stick appears to be bent
at the point where it pierces the surface of the water; and in
just the same way the rays of light are bent when they pierce into
the air. Fortunately, the mathematical theory of this atmospheric
bending of light is well understood, so that it is possible to
remove the effects of refraction from our results by a process of
calculation. In other words, we can transform our photographic
measures into what they would have been if no such thing as
atmospheric refraction existed. This having been done, all the arcs
on the plate should be exactly circular, and their common centre
should be the position of the pole among the stars on the night
when the photograph was made.
It is possible to facilitate the removal of refraction effects
very much by placing our photographic telescope at some point on
the earth situated in a very high latitude. The elevation of the
pole above the horizon is greatest in high latitudes. Indeed, if
Arctic voyagers could ever reach the pole of the earth they would
see the pole of the heavens directly overhead. Now, the higher up
the pole is in the sky, the less will be the effects of atmospheric
refraction; for the rays of light will then strike the atmosphere
in a direction nearly perpendicular to its surface, which is
favorable to diminishing the amount of bending.
There is also another very important advantage in placing the
telescope in a high latitude; in the middle of winter the nights
are very long there; if we could get within the Arctic. Circle
itself, there would be nights when the hours of darkness would
number twenty-four, and we could substitute complete circles
for our broken arcs. This would, indeed, be most favorable from
the astronomical point of view; but the essential condition of
convenience for the observer renders an expedition to the frozen
Arctic regions unadvisable.
But it is at least possible to place the telescope as far north
as is consistent with retaining it within the sphere of civilized
influences. We can put it in that one of existing observatories
on the earth which has the highest latitude; and this is the
observatory of Helsingfors, in Finland, which belongs to a great
university, is manned by competent astronomers, and has a latitude
greater than 60 degrees.
Dr. Anders Donner, Director of the Helsingfors Observatory, has
at its disposal a fine photographic telescope, and with this some
preliminary experimental "trail" photographs were made in 1895.
These photographs were sent to Columbia University, New York, and
were there measured under the writer's direction. Calculations
based on these measures indicate that the method is promising in
a very high degree; and it was, therefore, decided to construct a
special photographic telescope better adapted to the particular
needs of the problem in hand.
The desirability of a new telescope arises from the fact that we
wish the instrument to remain absolutely unmoved during all the
successive hours of the photographic exposure. It is clear that
if the telescope moves while the stars are tracing out their
little trails on the plate, the circularity of the curves will
be disturbed. Now, ordinary astronomical telescopes are always
mounted upon very stable foundations, well adapted to making the
telescope stand still; but the polar telescope which we wish to use
in a research fundamental to the entire science of astronomy ought
to possess immobility and stability of an order higher than that
required for ordinary astronomical purposes.
It is a remarkable peculiarity of the instrument needed for the
new trail photographs that it is never moved at all. Once pointed
at the pole, it is ready for all the observations of successive
generations of astronomers. It should have no machinery, no
pivots, axes, circles, clocks, or other paraphernalia of the usual
equatorial telescope. All we want is a very heavy stone pier,
with a telescope tube firmly fastened to it throughout its entire
length. The top of the pier having been cut to the proper angle of
the pole's elevation, and the telescope cemented down, everything
is complete from the instrumental side; and just such an instrument
as this is now ready for use at Helsingfors.
The late Miss Catharine Wolfe Bruce, of New York, was much
interested in the writer's proposed polar investigations, and
in October, 1898, she contributed funds for the construction of
the new telescope, and the Russian authorities have generously
undertaken the expense of a building to hold the instrument and the
granite foundation upon which it rests. Photographs are now being
secured with the new instrument, and they will be sent to Columbia
University, New York, for measurement and discussion. It is hoped
that they will carry out the promise of the preliminary photographs
made in 1895 with a less suitable telescope of the ordinary form.
THE MOON HOAX
The public attitude toward matters scientific is one of the
mysteries of our time. It can be described best by the single
word, Credulity; simple, absolute credulity. Perfect confidence
is the most remarkable characteristic of this unbelieving age.
No charlatan, necromancer, or astrologer of three centuries ago
commanded more respectful attention than does his successor of
to-day.
Any person can be a scientific authority; he has but to call
himself by that title, and everyone will give him respectful
attention. Numerous instances can be adduced from the experience
of very recent years to show how true are these remarks. We have
had the Keeley motor and the liquid-air power schemes for making
something out of nothing. Extracting gold from sea-water has been
duly heralded on scientific authority as an easy source of fabulous
wealth for the million. Hard-headed business men not only believe
in such things, but actually invest in them their most valued
possession, capital. Venders of nostrums and proprietary medicines
acquire wealth as if by magic, though it needs but a moment's
reflection to realize that these persons cannot possibly be in
possession of any drugs, or secret methods of compounding drugs,
that are unknown to scientific chemists.
If the world, then, will persistently intrust its health and wealth
into the safe-keeping of charlatans, what can we expect when things
supposedly of far less value are at stake? The famous Moon Hoax, as
we now call it, is truly a classic piece of lying. Though it dates
from as long ago as 1835, it has never had an equal as a piece of
"modern" journalism. Nothing could be more useful than to recall it
to public attention at least once every decade; for it teaches an
important lesson that needs to be iterated again and again.
On November 13, 1833, Sir John Herschel embarked on the Mountstuart
Elphinstone, bound for the Cape of Good Hope. He took with him a
collection of astronomical instruments, with which he intended to
study the heavens of the southern hemisphere, and thus extend his
father's great work to the south polar stars. An earnest student
of astronomy, he asked no better than to be left in peace to
seek the truth in his own fashion. Little did he think that his
expedition would be made the basis for a fabrication of alleged
astronomical discoveries destined to startle a hemisphere. Yet that
is precisely what happened. Some time about the middle of the year
1835 the New York _Sun_ began the publication of certain articles,
purporting to give an account of "Great Astronomical Discoveries,
lately made by Sir John Herschel at the Cape of Good Hope." It was
alleged that these articles were taken from a supplement to the
Edinburgh _Journal of Science_; yet there is no doubt that they
were manufactured entirely in the United States, and probably in
New York.
The hoax begins at once in a grandiloquent style, calculated to
attract popular attention, and well fitted to the marvels about
to be related. Here is an introductory remark, as a specimen:
"It has been poetically said that the stars of heaven are the
hereditary regalia of man as the intellectual sovereign of the
animal creation. He may now fold the zodiac around him with a
loftier consciousness of his mental supremacy." Then follows a
circumstantial and highly plausible account of the manner in
which early and exclusive information was obtained from the Cape.
This was, of course, important in order to make people believe
in the genuineness of the whole; but we pass at once to the more
interesting account of Herschel's supposed instrument.