260 PETER GUTHRIE TAIT 



simple distance action, a very formidable problem indeed to investigate the laws of 

 the propagation of electric or magnetic disturbance in a medium. And Maxwell 

 did not soon, or easily, arrive at the solution he now gives us. It is well-nigh twenty 

 years since he first gave to the Cambridge Philosophical Society his paper on Faraday's 

 Lines of Force, in which he used (instead of Thomson's heat-analogy) the analogy 

 of an imaginary incompressible liquid, without either inertia or internal friction, 

 subject, however, to friction against space, and to creation and annihilation at certain 

 sources and sinks. The velocity-potential in such an imaginary fluid is subject to 

 exactly the same conditions as the temperature in a conducting solid, or the potential 

 in space outside an electrified system. In fact the so-called equation of continuity 

 coincides in form with what is usually called Laplace's equation. In this paper 

 Maxwell gave, we believe for the first time, the mathematical expression of Faraday's 

 Electro-tonic state, and greatly simplified the solution of many important electrical 

 problems. Since that time he has been gradually developing a still firmer hold of 

 the subject, and he now gives us, in a carefully methodised form, the results of his 

 long-continued study.... 



It is quite impossible in such a brief notice as this to enumerate more than a very 

 few of the many grand and valuable additions to our knowledge which these volumes 

 contain. Their author has, as it were, flown at everything ; and, with immense spread 

 of wing and power of beak, he has hunted down his victims in all quarters, and from 

 each has extracted something new and invigorating for the intellectual nourishment 

 of us, his readers. 



In his review of Maxwell's remarkable little book Matter and Motion 

 (Nature, Vol. xvi, June 14, 1877) Tait was led into an interesting discussion 

 of the necessity for accuracy and for paying attention to the things which count. 

 He pointed his moral by quoting some sentences from recent text-books on 

 Natural Philosophy (which it had been his intention to review along with 

 Maxwell's book), and then proceeded to contrast them with Maxwell's 

 unpretentious volume. 



Clerk Maxwell's book is not very easy reading. No genuine scientific book 

 can be. But the peculiar characteristic of it is that (while anyone with ordinary 

 abilities can read, understand, and profit by it) it is the more suggestive the more 

 one already knows. We may boldly say that there is no one now living who would 

 not feel his conceptions of physical science at once enlarged, and rendered more 

 definite by the perusal of it... 



Clerk Maxwell's work, then, is simply Nature itself, so far as we understand it. 

 The peaks, precipices, and crevasses are all there in their native majesty and beauty. 

 Whoso wishes to view them more closely is free to roam where he pleases. When 

 he comes to what he may fear will prove a dangerous or impassable place, he will 

 find the requisite steps cut, or the needful rope attached, sufficiently but not 

 obtrusively, by the skilful hand of one who has made his own roads in all directions, 

 and has thus established a claim to show others how to follow. 



