806 



SCIENCE. 



[N. S. Vol. VIII. No. 206. 



Maxwell were slow in gaining acceptation. 

 "We must not omit to notice that in 1867 an 

 electro-magnetic theory of light was devel- 

 oped by Lorentz, but it was deduced from 

 different considerations. It was not until 

 the appearance of Maxwell's treatise, in 

 1873, that the attention of Continental 

 thinkers seems to have been drawn to the 

 new views. Already, however, had begun 

 the appearance of that series of papers 

 by the master hand of Helmholtz, which, 

 beginning with a powerful exposition 

 of the old electrodynamical theories, led 

 by successive steps to the development 

 of a theory similar to that of Maxwell, 

 which, as the life of the great German 

 drew to a close, uccame completely adopted 

 by him. Otherwise, however, there is little 

 to chronicle on the Continent until the 

 appearance of the treatise of Mascart and 

 Joubert, over a decade later than Max- 

 well's, showed that the seed had not fallen 

 upon stony ground. Let us accordingly 

 return to England, whither the center of 

 gravity of the mathematical development of 

 the subject was now transferred. 



The first paper to appear in the Philo- 

 sophical Transactions on Maxwell's theory 

 was fifteen years later, by Fitzgerald, in 

 1880, on the ' Electro-magnetic Theory of 

 the Reflection and Refraction of Light.' Here 

 we find an extension of the suggestion made 

 by Maxwell that the magnetic energy of the 

 field contains terms depending on vortical 

 motions about the lines of magnetic force, 

 and thus an attempt is made to explain the 

 phenomena of reflection of light from the 

 surface of magnets, discovered by Kerr. 



In 1881 followed a paper by Niven on 

 'The Induction of Currents in Infinite Plates 

 and Spherical Shells,' the former being a 

 subject which had been investigated by 

 Maxwell. In 1883 the subject of electrical 

 motions in spherical conductors was treated 

 by Lamb, who, however, makes the simpli- 

 fying hypothesis that the velocity of propa- 



gation of the inducing effect is infinite, that 

 hj'pothesis not materiallj' conflicting with 

 any experiments then made. In 1884 ap- 

 peared a paper by Larmor on the same sub- 

 ject. 



In 1884 appeared a very important paper 

 by Poynting on ' The Transfer of Energy in 

 the Electro- magnetic Field,' where, by a 

 direct application of Maxwell's theory, it 

 was shown how the route taken by the 

 energy in its passage from one plate to 

 another during variations of the field could 

 be described by the statement that the 

 energy flowed everywhere perpendicularly 

 to both the electric and magnetic field-vec- 

 tors, at a rate proportional to the area of 

 the parallelogram constructed on their 

 geometric representatives. Thus, according 

 to Poynting, the enei'gy passes from a dy- 

 namo to a motor not through the wires con- 

 necting the two, but through the air, being 

 guided in its course, however, by the wires. 

 The ideas of Poynting were extended by 

 Wien in two papers in Wiedemann's An- 

 nalen in 1892, as well as in a paper by J. J. 

 Thomson, on ' Faraday Tubes of Force.' 



In 1885 we have a still more important 

 paper by J. J. Thomson, on ' The Applica- 

 tion of Dj'namics to Physical Phenomena,' 

 in which, not especially the electrical ideas 

 of M9,xwell are developed, but rather the 

 method introduced by him of applying 

 Legrange's equations is extended to a great 

 number of phenomena. Singularly enough 

 the same sort of methods were soon to be 

 used by Helmholtz quite independently for 

 similar purposes. 



In 1SS7 Lauib attacked the more diffi- 

 cult problem than that of the sphere of ellip- 

 soidal current sheets, treating as a special 

 case the flow of currents in a circular disc, 

 and in 1888 the problem of induction of 

 currents in shells of small thickness was 

 treated by Burbury. The flow of current 

 in cylindrical conductors has been treated 

 by J. J. Thomson and Lord Rayleigh. lu 



