Notices respecting New Books. 307 



The general scope of the work will be inferred from the fore- 

 going account of its contents. The classification of the elements 

 may appear somewhat arbitrary, but there are good analytical 

 reasons for adopting this arrangement. The details of description 

 have all the lucidity and exactness which we are accustomed to 

 find in Mr. Crookes' writings. Although nearly a quarter of a 

 century has elapsed since the appearance of the first edition, there 

 is no falling off in power of treatment anywhere manifest in the 

 pages of the present Tolume, the completion of which is a matter 

 of congratulation both for the veteran author and the chemical 

 world. 



A Few Chapters in Astronomy. By Claudius Kennedy, M.A. 

 (Crown 8vo, 150 pp., 40 illustrations. London: Taylor & Francis, 

 1894.) 



The idea of this book is a very good one. Its object is to elucidate 

 more fully certain points which are merely touched on or only 

 imperfectly explained in works on Astronomy and Mechanics. In 

 the first Chapter we have an explanation of an optical illusion which 

 is frequently noticed, even by casual observers, but of which the 

 reason is not generally understood. This is the fact that a line 

 drawn at right angles to a line joining the horns of the crescent 

 Moon does not seem to pass through the Sun, as of course it really 

 does, but some distance above it. A similar illusion is seen in the 

 apparent downward curvature of meteor-tracks, and the apparent 

 curvature (in some cases) of a comet's tail when very long, as in 

 the Great Comet of 1882. The second Chapter deals with the 

 effect of the Earth's rotation on moving bodies, such as bodies 

 falling from a height, the flight of migrating birds, &c. The third 

 Chapter explains the effect of the Earth's rotation on projectiles. 

 The subject is very fully worked out, and in a very interesting 

 manner. In Chapter IV. an explanation is given of the principle 

 of Foucault's pendulum, a subject which is not sufficiently explained 

 in ordinary text-books on Astronomy, especially with reference to 

 places between the equator and the poles. Chapter Y. contains an 

 investigation of the position of high tide considered on dynamical 

 principles — a subject which is very imperfectly dealt with in most 

 works on Astronomy. In Chapter VI. we have a description of 

 various forms of the " Horizontal Pendulum," an instrument which 

 is not generally known, and which was devised for the purpose of 

 detecting by direct observation the Moon's differential tidal force. 

 Although sound in theory, this instrument does not seem to be 

 capable of giving any definite results in practice ; for, as Mr. Ken- 

 nedy says, " in most cases, at least, a gentle breeze pressing on the 

 side of a house would make the whole basement floor tilt to leeward 

 through an angle considerably greater than the greatest change in the 

 vertical by the Moon's tidal force." 



Chapters VII. and VIII. deal with the Moon's Variation and 



