FEBRUARY I1, 1897] 
NATURE 3 
339 
A STUDENT'S COURSE OF ASTRONOMY. 
Par M. B. Baillaud. Two vols. 
(Paris: Gauthier-Villars et Fils, 
Cours ad Astronomie. 
Pp. 280 and 509. 
1896.) 
T is a remarkable but no less accurate statement to 
say that the English student who wishes to dive 
deep into the inner circle of astronomical science must 
be dependent to a great extent on works produced 
outside this country. Oppolzer, Chauvenet, Watson, 
Klinkerfues, Olbers, and many others are books with which 
the serious reader must become well acquainted, to say 
nothing of works of a more advanced type, such as those 
by Tisserand, Gyldén, &c. 
Our literature deals, for the most part, with descriptive 
astronomy, in which the sun, moon and planets, &c., are 
lavishly described and illustrated: of these there is no 
limit. We are also well supplied with works on physical 
astronomy, but this branch of science is not included 
in the above remarks. 
In the two volumes before us, which we owe to the 
director of the observatory at Toulouse, M. Baillaud, we 
have an excellent course of astronomy for students. 
This work is not one devoted to descriptive astronomy, 
nor a treatise on celestial physics, but a mathematical 
course, presenting the reader with a survey of the various 
problems and modern methods of astronomy, including 
some of the more important results which have been 
obtained. 
In a brief and yet not too concise a manner, the author 
has brought together all the essential points that are 
necessary for a course in astronomy without extending 
any of them disproportionally. 
The first volume, we find, was published in the year 
1893. In this some of the theories applicable to the 
study of experimental science are handled, the knowledge 
of which is as important to physicists as to astronomers. 
Thus the author discusses the principles of the calculus 
of probabilities, showing how they may be applied to the 
theory of the errors of observation: the method of 
solving equations by the method of least squares is also 
here referred to in full. Next in order comes the general 
theory of optical instruments, which is investigated at 
some length, followed by the descriptions of the principles 
and problems involved in the action of lenses, prisms, 
eyepieces, various kinds of telescopes, &c. In the 
chapter on the different kinds of instruments used in 
making observations, chronometers, pendulums, levels 
and verniers are first in some detail described before the 
actual instruments, such as the meridian circle, equa- 
torial, altazimuth, &c., are dealt with. The equatorial 
coudé comes in for a good description, and, like the 
others, is well illustrated. The last two chapters are de- 
voted to the various methods of angular measurement, 
including the trigonometrical formule for facilitating 
the solutions of spherical triangles, and to the formulz for 
interpolation as suggested by the works of such men as 
Newton, Legrange, Gauss, and Jacobi. 
The second volume, which has only recently been 
published, contains as many as 500 pages, and may be 
considered the more important part of the work. 
The first few chapters are devoted to the solution of 
NO. 1424, VOL. 55 | 
such problems which may be considered here as pre- 
liminary to the main question of orbit determination. 
These include such subdivisions as systems of co- 
ordinates, refraction, parallax, aberration, precession, &c., 
each of which M. Baillaud has expounded with clear- 
ness and in sufficient detail to enable the reader to under- 
stand them. The apparent movements of the sun, 
together with those of the major planets, are next 
handled, the author discussing the various peculiarities 
of these motions, and how some of them may be de- 
pendent on the movements of the earth. This leads him 
naturally to deduce the laws of motion from observ- 
ation, eventually leading up to the problem of orbit 
determination. 
The chapter dealing with the methods of computation 
adopted at the present day for the determination of the 
orbits of comets, planets, &c., will be found expounded 
in a manner that is very helpful for the student. 
The author has kept strictly in view the main line of 
thought in the solution of the various problems, and has 
not overwhelmed the reader with the presence of too 
much detail on comparatively minor points. In this 
respect the student is at an advantage ; but, wherever 
necessary, he can always refer to that classical work of 
Oppolzer for further inquiry into minor details on any 
special question. 
In the chapter on perturbations, all the three well- 
known methods, which we owe to Bond, Encke, Hansen, 
and Tietjen’s modification of the last-mentioned, have 
been dealt with in a similar manner. 
The movements of the moon and of Jupiter’s satellites 
are next the subject of discussion, after which attention 
is devoted to the form and dimensions of the earth, a 
description being given of the various instruments and 
methods employed in such determinations. In addition 
to other problems, those relating to eclipses are referred 
to at some length; while the last chapter professes to 
give a brief summary of what is termed modern astro- 
nomy. This latter is found to be very scanty indeed, 
and is likely to do a student more harm than good. 
The lack of references of any kind, and the numerous 
omissions of importance are not likely to inspire con- 
fidence. Ina future edition it would be advisable either 
to make this part more complete, and add to its useful- 
ness by abundant references; or, on the other hand, 
omit it entirely, as it is quite unnecessary in a book of 
this kind. 
In the above notice, only a brief survey of the contents 
of these volumes has been made. It must be under- 
stood, however, that the author has dealt with several 
other problems of minor importance, their solutions 
being conspicuous by the conciseness of the methods 
employed. 
To sum up in a few words, the work asa whole may 
be said to form a serviceable contribution to the student’s 
library. Not only will it be used by those for whom it 
is specially intended, but English students, and especially 
those unacquainted with the German language, will find 
it an important help in their work. 
The text is relieved throughout by the insertion of 
many figures and woodcuts. 
