70 Notices respecting New Books. 



some extraordinary consequences were deduced, and these were 

 easily verified by experiment. 



This magnificent investigation shortly afterwards led to the 

 construction of apparatus by which very large visible vortex-rings 

 could be produced with certainty, and their mutual effects thus 

 directly demonstrated in the case of oblique as well as direct impact. 



Sir William Thomson, who had for years been trying to get rid 

 of the inadmissible postulate of infinitely hard particles (or atoms) 

 as the basis of material structures, and to account for their elasticity 

 by some species of motion, did not form his theory of Vortex Atoms 

 till the instant that he saw two of these large vortex-rings rebound 

 from one another after a collision, each quivering from the effects of 

 the blow. So that the theory was based by Sir W. Thomson, not 

 directly on Von Iielmholtz's splendid mathematics, but upon a 

 physical reproduction of their results, which indicated properties 

 not yet treated by mathematical processes. 



With remarkable rapidity he developed his theory, and commu- 

 nicated it in outline to the Royal Society of Edinburgh, to which 

 he has since given several other papers on the subject. These con- 

 tain, in some cases, extensions of the theory ; in others, modes of 

 meeting various difficulties as they arose. Several of these isolated 

 results of Sir W. Thomson's appear as verifications, in the course of 

 Mr. Thomson's work ; and it is obvious that the selection of this 

 subject for the Adams Prize Essay is due directly to the interest 

 excited by the theory of vortex atoms. 



Clerk-Maxwell, in a very remarkable essay (article Atom in the 

 new edition of the Encyc. Brit.), has brought prominently forward 

 the more salient points of this theory. He says : — " The greatest 

 recommendation of this theory, from a philosophical point of view, 

 is that its success in explaining phenomena does not depend on the 

 ingenuity with which its contrivers ' save appearances,' by introdu- 

 cing first one hypothetical force and then another. When the 

 vortex atom is once set in motion, all its properties are absolutely 

 fixed and determined by the laws of motion of the primitive fluid, 

 which are fully expressed in the fundamental equations. The 

 disciple of Lucretius may cut and carve his solid atoms in the hope 

 of getting them to combine into worlds ; the follower of Boscovich 

 may imagine new laws of force to meet the requirements of each 

 new phenomenon ; but he who dares to plant his feet in the path 

 opened up by Helmholtz and Thomson has no such resources. His 

 primitive fluid has no other properties than inertia, invariable den- 

 sity, and perfect mobility, and the method by which the motion of 

 this fluid is to be traced is pure mathematical analysis. The diffi- 

 culties of this method are enormous, but the glory of surmounting 

 them would be unique." 



Now Mr. Thomson's essay does not attempt any such investi- 

 gation as this. With him the diameter of the cross section of a 

 vortex-ring is always small in comparison with the diameter of the 

 ring itself ; and the mutual effect of two rings is treated only when 

 they do not approach within a distance exceeding many-fold the 



