XV 



form a confused multitude revolving, but not arranged in rings, and 

 constantly coming into collision. In the first case the mutual pertur- 

 bations of two rings may at length reach so great a magnitude as to 

 cause their destruction. In the second the destructive tendency is 

 more rapid, though it may be retarded by the particles settling down 

 into concentric rings. 



The most important contributions by Maxwell to the theory of 

 Elasticity are his paper on " Reciprocal Frames and Diagrams of 

 Forces," printed in the "Philosophical Magazine," 1864, and a 

 memoir under an almost identical title read to the Royal Society of 

 Edinburgh in 1870. These papers contain many beautiful theorems 

 on the geometry and mechanics of frameworks, interesting from a 

 purely theoretical point of view, but also leading to important 

 practical results. The memoir of 1870 constitutes a substantial 

 addition to the subject of elasticity, and some of the graphical methods 

 have been adopted and extended in works on engineering. The 

 mathematical treatment of the graphical method of internal stress in 

 this paper is remarkable for the beauty and symmetry of the expres- 

 sions and theorems obtained. 



In the foregoing sketch of Maxwell's writings we have grouped them 

 according to subjects rather than dates, thinking that in this way a 

 clear view would be gained of what he actually did in each subject. 

 We have thus been enabled to bring into prominence his greatest 

 memoirs and their connexions with one another. But there is still a 

 large number of mathematical papers, struck off from time to time, 

 and more or less 'important, of which we must omit any detailed 

 account. Among these are his papers on The Dynamical Top, on 

 Governors, on the General Laws of Optical Instruments, on Hamil- 

 ton's Characteristic Function. There is also a large class of miscel- 

 laneous essays on scientific subjects, which, though not marked by the 

 same intellectual power as his great memoirs, are yet possessed of 

 distinctive excellences of their own. This class comprehends (a) 

 Articles in the " Encyclopaedia Britannica," to which may be added an 

 elementary manual on Matter and Motion ; (b) his Addresses to the 

 British Association, to the London Mathematical Society, and the 

 Chemical Society, the Rede Lecture at Cambridge, and Lectures at the 

 Royal Institution; (c) Essays and Reviews contributed to "Nature." 



In some of these essays the author allowed himself a greater lati- 

 tude in the use of mathematical symbols and processes than in 

 others, the articles " Atom," " Capillary Attraction," " Constitution of 

 Bodies," " Diffusion," in the " Encyclopaedia Britannica," being, in 

 fact, brief treatises on these subjects treated mathematically. The 

 subjects of his lectures and addresses were, in the majority of cases, 

 one or other of those three departments of physics he had done so 

 much to extend — Colour Perception, Action through a Medium, 



