636 



SCIENCE 



[N. S. Vol. XLIV. No. 1140 



So far as I am aware neither Faraday in his 

 experimental researches nor Maxwell in his 

 mathematical treatment thereof, nor any one 

 else recently, ever proposed or performed an 

 experiment, excepting the experiments with 

 polarized light, to show that a direct connec- 

 tion existed between light and magnetism. 



At the end of Faraday's first period of bril- 

 liant discoveries or about 1841 various investi- 

 gators 1 had performed many experiments with 

 this end in view. 



In general these had taken the form of at' 

 tempts to magnetize bodies by exposure in par- 

 ticular ways to different kinds of radiations; 

 and a successful result had been more than 

 once reported only to be proven in error on re- 

 examination. 



Sir John Herschel was the first to indicate 

 the true path of procedure. He wrote : 



Induction led me to conclude that a similar con- 

 nection exists, and must turn up somehow or other, 

 between the electric current and polarized light 

 and that the plane of polarization would be de- 

 flected by magneto-electricity. 



Faraday had already discovered the nature 

 of this connection in 1834, but had considered 

 his experiment a failure. In 1845 after Her- 

 schel's remark he varied the original experi- 

 ment, with success, by placing a piece of heavy 

 glass between the poles of an excited electro- 

 magnet; and found that the plane of polariza- 

 tion of a beam of light was rotated when the 

 beam passed through the glass parallel to the 

 magnetic lines of force composing the field. 

 This constituted the discovery of the connec- 

 tion between light and magnetism. 



In 1851 Faraday wrote: 



It is not at all unlikely that if there be an 

 csther, it should have other uses than simply the 

 conveyance of radiation. 



This sentence has been considered the origin 

 of the electro-magnetic theory of light. 



The question which natural philosophers 

 had never ceased to speculate on, that of the 



i Morichini, of Home, 1813, Quart. Journal of 

 Science, XIX., p. 338. S. H. Christie, of Cam- 

 bridge, 1825, Phil. Trans., 1826, p. 219. Mary 

 Somerville, 1825, Phil. Trans., 1826, p. 132. 



manner in which electric and magnetic influ- 

 ences are transmitted through space, assumed 

 a definite form about the middle of the nine- 

 teenth century and issued in a rational theory. 

 It was at this point that the whole matter was 

 taken up and eventually theoretically solved 

 by Maxwell. He said: 



We can scarcely avoid the inference that light 

 consists in the transverse undulations of the same 

 medium which is the cause of electric and mag- 

 netic phenomena. 



At the time Maxwell did not examine 

 whether this relation was confirmed by experi- 

 ment. For years the electromagnetic theory 

 was beset with difficulties and was unfavorably 

 received by his most famous contemporaries. 

 Helmholtz after many years accepted it, but 

 Lord Kelvin, it seems, never did. 



It is quite interesting to note here that Lord 

 Kelvin in 1904 admitted that a bar magnet 

 rotating about an axis at right angles to its 

 length is equivalent to a lamp emitting light 

 of period equal to the period of rotation, giv- 

 ing his final judgment, however, that " the 

 so-called electro-magnetic theory of light has 

 not helped us hitherto." 



While pondering over the subject of terres- 

 trial magnetism, electricity and magnetism on 

 the night of Tuesday, March 7, 1916, the fol- 

 lowing thought came to me with such force 

 that I set it down in my diary. A copy is as 

 follows : 



I conceived the idea to try the effect of a con- 

 centrated sunlight on the magnetic needle or mag- 

 netized bar of any kind. The question being will 

 not the concentrated light lessen or strengthen the 

 magnetism of the magnet? 



In performing such an experiment arrange- 

 ment must be made so as to exclude the effects 

 of the absorbed energy appearing as heat. I 

 intended to try this as an experiment at some 

 convenient time in the hopes that some new 

 connection might be brought about concern- 

 ing the subject of light, electricity and mag- 

 netism and their mode of propagation. 



On Saturday, March 11, 1916, four days 

 afterwards, I chanced to see a newspaper clip- 

 ping regarding some work of Professor T. J. J. 

 See, of Mare Island, Cal. In this article Pro- 



