SCIENCE. 
125 
cases for such observatories to assume the positions of the 
fundamental stars, and to leave the farther improvement of 
their places to skillful astronomers who understand the 
theory of such work, and who carefully study' and become 
masters of their instruments. In these refined observations 
the refraction of light by our atmosphere also plays an im- 
portant part, and this question will need to be examined at 
every observatory that undertakes to do independent work. 
It is true that every new and good meridian instrument 
may, and perhaps ought, to contribute something towards 
removing constant errors, and giving us a more accurate 
knowledge of a star’s position ; but when this position is 
very well known, the only way for further improvement is 
through complete and careful observations, and their 
thorough reduction and discussion. 
In the observations of double stars but little had been 
done before the present century, and the labors of W. 
Struve form the real starting-point in this branch of astron- 
omy. These labors have been ably continued by his son, 
the present director of the Pulkowa Observatory, and the 1 
observations of these two astronomers, extending over a 
period of nearly sixty years, are ol the greatest value for 
our knowledge of the motions of the double stars. This is 
a branch of the science into which irregular workers are apt 
to enter, and where some of them have done good service ; j 
but it any amateur astronomer will compare his own work 
with that of the Struves, and will study the methods fol- 
lowed by them in determining their personal and instru- 
mental errors, and will emulate the steadiness with which 
they have followed out their purpose, he can do much to 
enhance the value of his labor. Here the observations are 
simple, and easily reduced, and the chief requisites are skill 
and patience on the part of the observer. He should not 
be discouraged because he obtains no immediate or great 
reward for his work, or public notice, or because some one 
who rants about the nebular hypothesis and kindred sub- 
jects, of which he knows nothing, is for a time the great as- 
tronomer of the day. The observer will learn finally that 
a good observation of the smallest double star, or of the 
faintest comet or asteroid, is worth more than all such 
vague talk. The observation has a positive value, how- 
ever small, but the physical theories of the universe, of 
which modern popular science is so productive, are gen- 
erally worse than useless. 
The first step towards a rational and trustworthy knowl- 
edge of our sidereal universe must come from a determi- 
nation of the distances of the stars. The solution of this 
problem was attempted soon after the Copernican theory ol 
our solar system was established, when it was seen that we 
have a long base line for our measures, or the diameter of 
the earth’s orbit, and it was supposed that the solution 
would be easy. These early trials were all failures, but 
they led to some very interesting and important discov- 
eries, such as Bradley’s discovery of the aberration of 
light ; to the knowledge of the fact that the determination 
of the parallaxes, or the distances of the stars, although 
simple in theory, is practically a difficult question ; and 
then to an improvement in the instrumental means of ob- 
servation, to a careful study of the methods of observation 
and the instruments, and to a recognition of the necessity 
of a complete and rigorous reduction of the observations. 
An examination of these early attempts is an instructive 
study. It is only about forty years ago that the solution of 
this problem was at last attained, and then only by the ap- 
plication of the most powerful instruments and the best ob- 
serving skill. An interesting result of the determinations 
of stellar parallax is obtained at once in the check it puts 
on speculations concerning the structure of the sidereal 
universe. The first astronomers who considered the par- 
allaxes of the stars very naturally assumed that the bright 
stars are nearer to us than the faint ones, and therefore 
they observed the bright stars for parallax. Now, while 
this assumption may be true as a general statement, the 
actual determinations of parallax show that some of the i 
faint stars which are not visible to the naked eye are much 
nearer to us than the brightest stars of our northern sky. 
Again it was assumed that a large proper motion is a cer- 
tain index of a star’s nearness to us ; but observation shows 
that this also may be an erroneous assumption. This is a 
problem whose solution is only just begun, but already we 
know enough of its difficulties to see that we need the most 
powerful micrometrical apparatus that can be brought into 
use. The invention of some micrometer that, while as ac- 
curate as the present filar micrometer, would give the ob- 
server a much greater range of observation, and enable 
him to select suitable stars of comparison, is something 
much to be desired. At present the heliometer seems to 
be the best instrument for observations of this kind. 
Formerly it was thought that photography would furnish a 
good method for such delicate determinations ; but so far 
the photographic methods have not given the necessary de- 
gree of accuracy in the measurements, and the astronom- 
ical use of photography is confined mostly to descriptive 
astronomy, where, especially in solar eclipses, it has ren- 
dered excellent service. Closely connected with the par- 
allaxes of the stars and their proper motions is the interest- 
ing question of determining their motions to or from our 
sun, according to the theory of Doppler. Here likewise 
the numerical determinations are so discordant, that we 
cannot have much confidence in the results. In both these 
cases we need more powerful apparatus, and a complete 
and thorough investigation of the methods of observation. 
Perhaps some of the large instruments now constructing 
may be employed in these methods, and we may soon have 
belter results. 
A great advance has been made in catalogueing the fainter 
stars. This work was begun by the French astronomers 
nearly a century ago, and was continued by Bessel, Arge- 
lander, and others. An important step towards the com- 
pletion of this work was taken by Argelander and his as- 
sistants in their great catalogue of the approximate posi- 
tions of 324,198 stars, which was finished in 1861. This 
census of the stars will soon be extended, we hope, over 
the whole heavens ; and it already forms the groundwork 
for the great zone observations of stars now going on in 
Europe and in this country, and which must be nearly 
finished. These observations will doubtless reveal many 
interesting cases ol the proper motion of the stars, and will 
certainly form the basis for a knowledge of the motion of 
our solar system in space, and for sidereal astronomy gen- 
erally, such as we have never had before. Our American 
observatories can render a good service by observing stars 
of southern declination, since our observatories are ten or 
twelve degrees farther south than those of Europe, and thus 
have an advantage of position which ought to be made use 
of; and which may serve to unite into a harmonious sys- 
tem the observations made in the northern and southern 
hemispheres. The work of mapping the very faint stars 
near the ecliptic has also been greatly extended, and it is 
to this extension that we owe the rapid increase in the 
number of the small planets between Mars and Jupiter. 
But besides aiding in the discovery of the asteroids, accu- 
rate charts of the small stars have a permanent value in 
giving us a knowledge of the heavens at their epoch, and 
also some idea of the distribution of the stars in space. 
It is an interesting question whether, among the thousands 
of nebulae that are scattered over the heavens, any of them 
show changes of form or of brightness. These objects 
seem to be at least as distant as the stars, and as they have 
sometimes an area of several degrees, they must be bodies 
of an enormous extent. That changes are going on in 
these bodies seems probable, but to be visible at such dis- 
tances the changes must be very great. In this case there 
is need of much caution in the discussion of the drawings 
made at different epochs, and by different astronomers with 
telescopes of different power; since the nebulae change 
their appearance with the telescope used, with different 
conditions of the air, and with a variation of their altitude 
above the horizon. Here the excellent photometers that 
have been recently invented, and which are being so well 
applied to the determination of the brightness of the stars, 
may give us assistance. Perhaps also new drawings of the 
nebulae, and their criticism and discussion, and a full re- 
cognition of the difficulties of making such drawings, will 
soon lead to a decision of the question of their change of 
form. Since the study of the light of the stars with new 
and improved photometers has now become a specially, we 
may look for more exact and continued observations of the 
variable stars. This is a matter of which we know but 
little, and it is one where a persevering observer may do 
