396 Notices respecting New Books. 



closed system. Hence the magnetic and current-systems, if 

 equivalent in air, are equivalent in a medium which does not 

 penetrate through any portion of the space occupied by the 

 magnetic substance. 



It is particularly to be noticed that, while in air any two of 

 the infinite number of magnetic shells equivalent to two closed 

 currents exercise the same attraction upon one another, this is 

 no longer true when they are immersed in the medium fj,. 

 Then each pair exercises the same attraction as the two cur- 

 rents when the corresponding diaphragms S are drawn in the 

 shape of the magnetic shells. 



An experiment made by me in the Cavendish Laboratory 

 last June confirms, as far as it goes, Dr. Lodge's view ; but, 

 fearing to make my letter too long for insertion, I must post- 

 pone any account of it for the present. 



I am, Gentlemen, 



Your obedient servant, 

 October 20, 1882. E. B. SARGANT. 



XLIV. Notices respecting Neio Boohs. 



The Concepts and Theories of Modern Physics. By J. B. Stallo. 

 London : Kegan Paul and Trench. 1882. 

 rpO write an adequate criticism of this book would involve writing 

 -*- a book of equal size. In the present review it is intended to 

 make clear the standpoint from which the author speaks, and the 

 general conclusions reached, rather than to enter into a detailed 

 criticism of these conclusions. The failure to appreciate the posi- 

 tion from which the, author writes has already led to some mis- 

 understanding and not a little confusion. It is stated in the preface 

 that the work is intended " as a contribution not to physics, nor 

 certainly to metaphysics, but to the theory of cognition." There is 

 probably no word which is more quoted and less understood than 

 the word " metaphysics." It is used by hardly any two writers in 

 the same sense ; and it is not too much to say that in many cases 

 it is merely used as a term of abuse without any clear conception 

 of its meaning. As in the present work this word is constantly 

 used, and, moreover, as the author's main purpose is to show that 

 certain scientific theories are in reality metaphysical, it will be im- 

 portant to understand precisely the signification which he puts 

 upon the word. It is abundantly evident from the whole book that 

 the subject which Mr. Stallo condemns, and rightly condemns, under 

 the name of metaphysics is that which is far better designated by 

 outology ; and in fact he himself frequently uses these terms as 

 synonymous. The assumption of fictitious entities as causes, the 

 belief that " the true nature of things can be discovered only by 

 divesting them of their relations — that to be truly known they 

 must be known as they are in themselves in their absolute essence," 

 and in fact the whole procedure of ontology, is what is meant by 



