778 SCIENCE PROGRESS 



readers, and so might have been more fully described, is dismissed in a few 

 sentences. 



The book has been written at a rather unfortunate time, since a few months 

 after its publication a paper has appeared which seems to show the cause of many 

 of the inconsistencies between different experiments, and to be likely to influence 

 profoundly the whole field of research. We refer to the work of Fredenhagen 

 and Kiistner, published in the Physikalische Zeitschrift for January 1914, where 

 it is shown that pure zinc, freed from gases by scraping in a very high vacuum, 

 gives no photoelectric effect at all. If this work, when extended, shows that 

 other substances too, when absolutely free from gases, give no photoelectric 

 effect, then the old work will obviously have to be carefully revised. 



Dr. Allen's book is useful as giving a correct account of most of the work 

 which has been done on the subjects he treats, while leaving criticism of it largely 

 to the reader. In the treatment of the photoelectric effect on water there is no 

 mention of Obolensky's paper (Annalen der Physik, iv. 39, 1912, p. 961), which 

 contains the best measurements, and explains previous inconsistencies, Lenard's 

 latest work on phosphorescence is not touched, and one or two other papers of 

 some interest are neglected. A few such omissions are almost inevitable ; on the 

 whole the book is fairly complete, and can be recommended to those interested 

 in the subject as being the only account to be found in English (excepting 

 J. J. Thomson's famous book on the conduction of electricity in gases, which 

 only goes up to 1906) where the researches in this region are collected. 



E. N. da C. A. 



Definitions in Physics. By Karl Eugen Guthe, Professor of Physics in the 

 University of Michigan, and Dean of the Graduate Department. [Pp. 

 vii -f- 107.] (The Macmillan Company, 1913. Price y. 6d. net.) 



The whole book is taken up with a series of bright "snappy" sentences, giving 

 in two or three lines definitions of physical conceptions and quantities, such as 

 light, surface tension, electron, and so on. A few examples will make clear the 

 nature of the information supplied : " Interference is the destructive or reinforcing 

 action of different systems of waves upon each other," " Magnetism is the name 

 of a hypothetical substance producing attraction or repulsion between magnetic 

 bodies by action at a distance," " Electrolysis is the decomposition of an elec- 

 trolyte." There are about a hundred pages of this kind of thing, in the course 

 of which we are told that a rays "are identical with ordinary canal rays" 

 (reviewer's italics). 



We cannot imagine any useful purpose to be served by such a book, which 

 would seem to encourage as part of a scientific education the parrot-like learning 

 of a few hundred " definitions," necessarily incomplete, generally meaningless as 

 they stand, and sometimes misleading, if not actually wrong. 



E. N. DA C. A. 



The Chemistry of the Radio-elements. Part. II. The Radio-elements and 

 the Periodic Law. By Frederick Soddy, F.R.S. [Pp.46.] (London: 

 Longmans, Green & Co. Price 2s. net.) 



The importance of this book is not to be gauged from its size ; for it embodies a 

 classification, with its resulting theories, which will probably prove to be the 

 greatest stride made in inorganic chemistry since Mendeleeffs time. As with 

 other cases of the kind, earlier workers had glimpses of the truth, but to Fajans 



