Notices respecting New Books. 2G1 



series of images corresponding to the two sets of waves ; 

 the laws for the image series due to the extraordinary 

 waves correspond to those for lenses of isotropic substance, 

 and the expressions are found for the dioptric power. The 

 question of the use of crystal components in lens systems is 

 also considered briefly. 



Physical Laboratory, 

 University of Toronto, 

 May '2, 1916. 



XXXI. Notices respecting New Books. 



An Introduction to the Mechanics of Fluids. By Edwin H. Bakton, 

 D.Sc, F.B.S.E. Pp. xiv + 249. With diagrams and examples. 

 Longmans, Green & Co. : London. 1915. 6s. net. 



TT is somewhat difficult to write a book on elementary mechanics 

 -*- which shall present any very novel feature. But there are traits 

 of this one which are certainly novel, and, which is still better, novel 

 in an attractive way. One of these characteristics is that while 

 the calculus is avoided it is replaced, not by the very artificial 

 methods with which we are all so familiar, but by a method of 

 summation which forms one of the best possible introductions to 

 the calculus itself. This is a very great gain. The most inter- 

 esting part of the book is that dealing with applications of the 

 mechanics of fluids in technical practice. We have never come 

 across so complete and satisfactory an account of the different 

 forms of suction and compression pumps, rams, Bourdon and 

 other gauges, water-wheels, presses, lifts, cranes, turbines, drills, 

 brakes, <fcc. We commend this part in particular to school 

 teachers ; nothing could be better calculated to stimulate aud at 

 the same time to instruct the youthful mind. 



The introduction to mechanics is in general very logical. One 

 or two very minor points made the reviewer hesitate for a moment. 

 The first page scarcely brings out the fact that a liquid opposes 

 no permanent resistance to change of shape. To talk of very 

 small resistances scarcely meets the case. In consequence of 

 this inadequate statement it will not be evident (as it is stated 

 to be) that viscosity " need not enter into our account when 

 considering any fluids at rest in equilibrium." 



Again, is it a matter of such indifference what definitions are given 

 of mass and force ? The inadequacy of Xewton's treatment of 

 mass arises from the fact that although the masses (or quantities 

 of matter) of the same substance may be taken as proportional 

 to their volumes, we cannot pass from these cases to cases in 

 which the material is different. 



It must further be remembered that those who are driven to 

 define force with reference to our muscular sensations are not 

 only illogical, but are wrong; because, as every psychologist 

 knows, our sensations of force are not proportional to the equivalent 

 forces measured mechanic-all v. 



