Elements of Astronomy

Abstract

THIS is one of the books in which astronomy seems to be regarded as a subject which is to be studied much in the same way as one would take up an additional book of Euclid. It abounds in definitions, propositions, and corollaries; the diagrams of instruments scarcely give any ideas of what they are intended to represent; and the descriptive part of the subject might have been omitted without much sacrifice. The ground covered is that which is ordinarily understood by an elementary treatment of mathematical astronomy, dealing chiefly with the considerations relating to the positions, movements, dimensions, and distances of the various heavenly bodies, but includes also some very scanty references to their telescopic appearances. On the whole, the various points are clearly, though shortly, explained, but there is much to suggest that the author would be all the better for some little observatory practice; for example, his method of determining the angular value of a micrometer by means of the sun (p. 48) is scarcely practicable, and a sun-spot 13,000 miles long is by no means to be classed as one of the largest spots (p. 68). It may be pointed out, also, that a single observer, by observing at intervals of twelve hours, gets better results for the parallax of Mars than two working in the way indicated on p. 115. A ship's mean time at sea, too, is usually determined by one observation near the primevertical, and not by the method of equal altitudes.

Elements of Astronomy.

By G. W. Parker (London: Longmans, Green, and Co., 1894.)