80 ScientifiG Litelligence. 



senting a law may be readily seen from the following typical 

 illustration: 



*^ Coulomb's Law. 



The electric intensity of a point p close to the surface of a 

 conductor surrounded by air is at right angles to the surface. It 

 is equal to 47ro- where <t is the surface density of the electrifica- 

 tion. If the surface of the conductor is in contact with a dia- 

 electric of specific inductive capacity K, then the electric 

 intensity at the point p is, 



i^hom^on, Elements of Electricity and Magnetism, pp. 36, 122.)'* 

 The text proper is followed by a bibliographical list of authors, 

 reference books, and journals, and by an index. The publishers 

 have taken pains to make the volume as convenient as possible 

 by using clear type, matt paper, and limp leather binding. 



Although the book is useful and much can be said in its favor, 

 nevertheless it seems desirable and fair to point out a few of its 

 general and specific defects. In the first place, a reference book 

 of this kind should be as full and complete as possible. It fails 

 in this respect since no mention is made of the laws and funda- 

 mental phenomena of radio-activity (save only the "heat pro- 

 duced by radium"), spectroscopy, and X-rays. 



Again, with regard to details, there is room for improvement. 



[a) The formula given (p. 187) for Newton's rings is a purelj^ 

 mathematical relation between the sagitta, the associated semi- 

 chord, and the radius of a circle, when the square of the sagitta 

 is negligible. The formulae for the bright and dark rings are 

 not even suggested. It would be just as fair to imply that 



r' . 

 " t = -^pr " is the formula for a thin lens, since it is often used as 

 2R ' 



a lemma in deriving the lens equation by the wave-front method. 



[b) The statement of Fermat's principle of least time (p. 167) 

 refers only to the minimum and thus gives no clue to the cases 

 involving maxima of time. (c) There are two unfortunate 

 typographical errors on page 51. The mass per unit length of a 

 string or wire is specified as "grains per cm." instead of grams 

 per cm. The formula for the frequency of a transversely vibrat- 

 ing cord has 21 omitted under the symbol 1. h. s. u. 



II. Geology and Natural History. 



1. United States Bureau of Mines ; Van H. Manning, Direc- 

 tor. — Recent publications from the Bureau of Mines (see earlier, 

 vol. xliii, pp. 86, 87) include the bulletins whose titles are given 

 below ; also a series of Technical Papers and Miners' Circulars. 

 It is announced that owing to the expense involved in the pre- 

 paration and publication of the bulletins and the limited 

 printing funds available^ it has been necessary to place a definite 



