IT is difficult to decide what limits an author should set himself in writing a text-book on this subject. Gravitational astronomy on the one hand and descriptive and general astronomy on the other should be, for the most part, omitted. A more difficult question arises as to what details of practical astronomy should be included. It seems to us that the aim of such a book should be to show how the geometrical positions of stars and other heavenly bodies are defined and accurately determined, and how these positions vary with the place and time of observation, and from such causes as refraction and aberration. Some description of the more important instruments, e.g. the transit circle, the equatorial, theodolite, and sextant, should be included, and preferably in connection with the class of astronomical problem to which they are applied, and the geometrical problems to which they give rise or which arise in connection with them. The excellent little book, written by Sir Robert Ball in 1877, fulfils this condition. Godfrey's “Astronomy” is incomplete and antiquated, but in this way is an admirable manual for students. A Treatise on Spherical Astronomy. By Sir Robert Ball Pp. xii+506. (Cambridge: University Press, 1908.) Price 12s. net.
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