234 Mr. J. J. Thomson on the 



the influenco of time, mass, and temperature on chemical 

 combination. Bunsen, Crafts and Meier, Friedel, Guldberg 

 and Waage, Horstmann, Lemoine, Victor Meyer, and others 

 have experimentally investigated one or other of these 

 points. The researches of M. Lemoine on the combination 

 of hydrogen and iodine seem to be the most complete study 

 of a chemical combination which we possess; and I am in- 

 debted to M. Lemoine's two papers in the Annates de Chimie 

 et de Physique, 5 me serie, t. xii. and xxvi., for most of the 

 experimental data quoted in this paper. Messrs. Guldberg 

 and Waage, M. Lemoine, M. Horstmann, and Prof. Willard 

 Gibbs have given theories of chemical combination which 

 seem to agree well with the results of experiments. 



It is unfortunate that the only case which we can in- 

 vestigate mathematically on direct dynamical principles, viz. 

 the combination of gases, is the one where the difficulties of 

 chemical manipulation are greatest. The following theory 

 is only intended to apply to gases. Before going further it 

 will be well to state what we suppose takes place during 

 chemical combination, for although most of what follows 

 will apply to any theory of the constitution of bodies, 

 yet as it is a great help to be able to form a definite * Vor- 

 stellung " of what takes place, we shall assume that the 

 atoms of bodies consist of one or more vortex-rings, and take 

 the view of chemical combination expressed by the following 

 extracts from a book written by the author of this paper 

 ('On the Motion of Vortex-Rings/ pp. 114, 115, 116):— 

 (i When two" vortex-rings of equal strength with (as we shall 

 suppose for the sake of simplicity) their planes approximately 

 parallel to each other and approximately perpendicular to the 

 line joining their centres, are moving in the same direction, 

 and the circumstances are such that the hinder ring overtakes 

 the one in front, then if, when it overtakes it, the shortest 

 distance between the circular lines of vortex-core of the rings 

 be small compared with the radius of either ring, the rings 

 will not separate, the shortest distance between their central 

 lines of vortex-core will remain approximately constant, and 

 these circular lines of vortex-core will rotate round another 

 circle midway between them, while this circle moves forward 

 with a velocity of translation which is small compared with 

 the linear velocity of the vortex-rings round it. We may 

 suppose that the union or pairing in this way of two vortex- 

 rings of different kinds is what takes place when two elements, 

 of which these vortex-rings are atoms, combine chemically, 

 while if the vortex-rings are of the same kind, this process is 

 what occurs when the atoms combine to form molecules. If 



