REVIEWS 335 



at the present stage it is doubtful if classification has any particular value. In 

 connection with Brownian movement, which has in recent years served to bring 

 the colloidal and emulsoidal state into close relation to physics, a very useful table 

 is given of the values of the molecular constants {e.g. the Avogadro number and 

 the electronic charge), determined by very different methods. The list, however, 

 should have contained the results of Millikan's oil-drop method. The phenomenon 

 of cataphoresis, to which Dr. Burton himself has contributed much, is particularly 

 well treated. It includes a comprehensive table of the mobilities of suspensions, 

 suspensoids, and emulsions, an interesting comparison being drawn between these 

 mobilities and those of electrolytic ions. The still unsolved question of the source 

 of the charge carried by a colloidal particle is discussed both from a physical and 

 a chemical point of view. The author himself evidently favours a chemical 

 explanation, and much of the research recently carried out points strongly in this 

 direction. It must be confessed, however, that the data are still too meagre to 

 allow one to come to a definite conclusion on the matter. As the author says in 

 concluding the monograph : " In spite of the immense amount of work that has 

 been done during the last fifteen years, it is quite apparent, that both from a 

 theoretical and a practical point of view, there still is need for much additional 

 research before one would be able to suggest with any degree of satisfaction a 

 general theory of the colloidal state." This is somewhat disappointing, but its 

 realisation ought to be a strong incentive to further research in this great branch 

 of physical chemistry. 



W. C. McC. Lewis. 



Text-Book of Practical Physics. By H. S. Allen, M.A., D.Sc, and 

 H. MOORE, A.R.C.Sc, B.Sc. [Pp. xv + 622, with 297 diagrams.] 

 (London : Macmillan & Co., 1916. Price 8s. bd. net.) 



There is unquestionably an opening for a standard work on Practical Physics for 

 students who are not sufficiently advanced to use Watson's well-known text-book, 

 and Dr. Allen and Mr. Moore's book is admirably designed to fill the gap. It has 

 been based on the manuscript instruction sheets used in the Physical Laboratory 

 at King's College, London, and includes all the experiments likely to be required 

 in a Pass or Honours Intermediate Course. No previous knowledge of practical 

 work is assumed ; but it would not be suitable for those whose theoretical know- 

 ledge is much below matriculation standard. The theoretical as well as the 

 practical side of the experiments is dealt with at considerable length, with the 

 inevitable result that the book is rather bulky and expensive ; it is, however, also 

 issued in three separate parts. These divisions are : I, Properties of Matter, 

 including an excellent course in Practical Mechanics intended, in the first instance, 

 for the benefit of Engineering Students in the University of London ; II, Sound, 

 Light, and Heat ; and III, Magnetism and Electricity. Save in a few unavoidable 

 cases the apparatus described is all of that simple description which, calling for 

 a certain amount of care and skill to give accurate results, is best suited for 

 students at this stage of their work. 



The book is very thorough and very complete, but on examining it closely 

 a certain sense of disappointment is produced by the fact that it is also rather 

 ordinary. There are none of the special refinements either in manipulation or in 

 modes of calculation that might be expected from authors of such experience ; 

 there is nothing, or very little, that is not well known to every experienced teacher ; 

 on the contrary there are just a few things which all those intent on the best 



