MAXWELL'S SCIENTIFIC WORK 263 



is one of the most remarkable of his investigations. Maxwell reproduces in it, by 

 means of a special set of assumptions, the equations already given by Stokes. He 

 applies them to a number of very interesting cases, such as the torsion of a cylinder, 

 the formation of the large mirror of a reflecting telescope by means of a partial vacuum 

 at the back of a glass plate, and the Theory of Orsted's apparatus for the compression 

 of water. But he also applies his equations to the calculation of the strains produced 

 in a transparent plate by applying couples to cylinders which pass through it at right 

 angles, and the study (by polarised light) of the doubly-refracting structure thus 

 produced. He expresses himself as unable to explain the permanence of this structure 

 when once produced in isinglass, gutta percha, and other bodies. He recurred to the 

 subject twenty years later, and in 1873 communicated to the Royal Society his very 

 beautiful discovery of the temporary double refraction produced by shearing in viscous 

 liquids. 



During his undergraduateship in Cambridge he developed the germs of his future 

 great work on "Electricity and Magnetism" (1873) in the form of a paper "On 

 Faraday's Lines of Force," which was ultimately printed in 1856 in the "Trans, of 

 the Camb. Phil. Society." He showed me the MS of the greater part of it in 1853. 

 It is a paper of great interest in itself, but extremely important as indicating the 

 first steps to such a splendid result. His idea of a fluid, incompressible and without 

 mass, but subject to a species of friction in space, was confessedly adopted from the 

 analogy pointed out by Thomson in 1843 between the steady flow of heat and the 

 phenomena of statical electricity. 



After a fairly exhaustive account of Maxwell's principal contributions to 

 scientific literature, Tait continued : 



Maxwell has published in later years several additional papers on the Kinetic 

 Theory, generally of a more abstruse character than the majority of those just 

 described. His two latest papers (in the Phil. Trans, and Camb. Phil. Trans, of last 

 year) are on this subject : one is an extension and simplification of some of Boltzmann's 

 valuable additions to the Kinetic Theory. The other is devoted to the explanation of 

 the motion of the radiometer by means of this theory. Several years ago (Nature, 

 Vol. XII, p. 217), Prof. Dewar and the writer pointed out, and demonstrated 

 experimentally, that the action of Mr Crookes' very beautiful instrument was to be 

 explained by taking account of the increased length of the mean free path in rarefied 

 gases, while the then received opinions ascribed it either to evaporation or to a quasi- 

 corpuscular theory of radiation. Stokes extended the explanation to the behaviour of 

 disks with concave and convex surfaces, but the subject was not at all fully investigated 

 from the theoretical point of view till Maxwell took it up. During the last ten years of 

 his life he had no rival to claim concurrence with him in the whole wide domain of 

 molecular forces, and but two or three in the still more recondite subject of electricity. 



" Everyone must have observed that when a slip of paper falls through the air, its 

 motion, though undecided and wavering at first, sometimes becomes regular. Its 

 general path is not in the vertical direction, but inclined to it at an angle which 

 remains nearly constant, and its fluttering appearance will be found to be due to 



