n8 THE POPULAR SCIENCE MONTHLY. 



one on the " Theory of Rolling Curves," and the other on the " Equi- 

 librium of Elastic Solids." 



During his college course in Cambridge he developed the germs of 

 his future important work on electricity and magnetism, in a paper on 

 " Faraday's Lines of Force," and five other papers on the same sub- 

 ject were contributed by him to the " Philosophical Magazine " during 

 1861 and 1862. Only a few months after obtaining his Cambridge 

 degree in 1854, he contributed to the Cambridge Philosophical So- 

 ciety a remarkable paper on the " Transformation of Surfaces by Bend- 

 ing." In 1857 his paper on the " Motions of Saturn's Rings " ob- 

 tained for him the Adams prize in the University of Cambridge. He 

 received in 1860 the Rumford medal from the Royal Society for his 

 " Researches on the Composition of Colors " and other optical papers. 

 The subject of color Professor Maxwell has treated with great success, 

 both experimentally and theoretically, his papers on the subject ex- 

 tending from 1855 to 1872. His important paper on a " Dynamical 

 Theory of the Electro-magnetic Field," in which he endeavored to 

 explain electric and magnetic forces by means of stresses and motions 

 of the medium, and thus do away with the notion of action at a dis- 

 tance, was read before the Royal Society in 1864, and printed in the 

 " Transactions " of that year. His contributions to the Kinetic theory 

 of gases form one of the most important and valuable of his investiga- 

 tions. His first paper on this subject appeared in the " Philosophical 

 Magazine" of 1860, and he at different times since published various 

 others. Before him, Clausius had made a great advance by his ex- 

 planation by this theory of the relation between the volume, tempera- 

 ture, and pressure of a gas, the cooling of it by expansion, and the 

 slowness of diffusion and conduction of heat in it. An investigation 

 was also made by him of the relation between the length of the mean 

 free path of a particle, the number of particles in a given space, and 

 their least distance when in collision. Maxwell by an investigation of 

 the collisions of a number of perfectly elastic spheres, first when they 

 are all of the same mass, and then when they are of different masses, 

 reached the law of Gay-Lussac, that in a unit of volume there is the 

 same number of particles in all gases when at the same temperature 

 and pressure. He also explained gaseous friction, and showed that the 

 coefficient of viscosity is independent of the density of the gas. The 

 approximate length of the mean free path was first deduced by him 

 from data furnished by Stokes. 



Pursuing the same subject, he made a few years later a valuable 

 series of experimental investigations on the viscosity and internal fric- 

 tion of air and other gases, the results of which were brought to the 

 attention of the Royal Society in 1866. A paper on " A Method of 

 making a Direct Comparison of Electrostatic with Electro-magnetic 

 Force, with a Note on the Electro-magnetic Theory of Light," was also 

 presented to that body in 1868. He took great interest in graphical 



