Chemistry and Physics. 453 



the book will be particularly useful to those interested in these 

 branches of science. h. l. w. 



5. Manual of Chemical Analysis as Applied to the Assay of 

 Fuels, Ores, Metals, Alloys, Salts, and other Mineral Products y 

 by Eugene Prost ; translated by J. Ckuickshank Smith. 8vo, 

 pp. 300. London, Maclaren & Sons; New York, D. Van Nos- 

 trand Company, 1904. — The object and scope of this work are 

 set forth in the title. It should serve as a useful book of refer- 

 ence for analytical chemists engaged in technical work, for many 

 of the methods of analysis are well selected and carefully 

 described. A good feature of the book is the introduction of 

 typical analyses of many commercial products, which give the 

 chemist an idea of the ingredients to be looked for as well as the 

 extent to which they are liable to occur. The book may be criti- 

 cized on account of failing to include certain useful and reliable 

 methods. For instance, Drown's method for the determination 

 of silicon in pig iron is not given, while tared paper filters are 

 recommended for weighing precipitates in cases where the Gooch 

 crucible would give far better service, and other antiquated 

 features from an American point of view are to be noticed. Not 

 all of the methods are described in such a way that they would 

 give a satisfactory degree of accuracy when implicitly followed, 

 and in some cases the directions are decidedly lacking in com- 

 pleteness, or the methods are faulty in principle. The book is, 

 therefore, not a perfect one, although it contains much that is 

 useful. It seems unfortunate that the translator should have 

 employed incorrect chemical nomenclature in some cases ; for 

 instance, chloride of soda for sodium chloride. h. l. w. 



6. Radiation Pressure. — Professor Poynting discusses simple 

 methods of showing the pressure of light, and applies his theory 

 of the stream of momentum. Theory and experiment seem to 

 indicate that when a source is sending out waves it is pouring 

 out with them forward momentum as well as energy, the momen- 

 tum being manifested in the reaction, the back pressure against 

 the source, and in the forward pressure when the waves reach an 

 opposing surface. The wave train may be regarded as a stream 

 of momentum traveling through space. Radiation pressure has 

 not succeeded in explaining the repulsion of comet's tails. Pro- 

 fessor Poynting suggests the following explanation of Saturn's 

 rings : Let us imagine that a small sun while still radiating much 

 energy on its own account has captured and attached to itself as 

 satellite a cometary cloud of dust. Then, if the cloud consists 

 of particles of different sizes, while all will tend to draw into the 

 primary, the larger particles will draw in more slowly. But if 

 the larger particles are of different sizes among themselves, they 

 will have different periods of revolution, and will gradually form 

 a ring all round the planet on the outside. Meanwhile the finer 

 particles will drift in, and again differences in size will corre- 

 spond to difference in period and they too will spread all around, 

 forming an inner fringe to the ring. If there are several grades 



