FAEADAY. 413 



rausch above all, the researches of Clerk Maxwell on 

 the Electro-magnetic Theory of Light point to that 

 wonderful and mysterious medium, which is the vehicle 

 of light and radiant heat, as the probable basis also of 

 magnetic and electric phenomena. The hope of such a 

 connection was first raised by the discovery here re- 

 ferred to.* Faraday himself seemed to cling with par- 

 ticular affection to this discovery. He felt that there 

 was more in it than he was able to unfold. He pre- 

 dicted that it would grow in meaning with the growth 

 of science. This it has done; this it is doing now. 

 Its right interpretation will probably mark an epoch 

 in scientific history. 



Rapidly following it is the discovery of Diamag- 

 netism, or the repulsion of matter by a magnet. Brug- 

 mans had shown that bismuth repelled a magnetic 

 needle. Here he stopped. Le Bailliff proved that 

 antimony did the same. Here he stopped. Seebeck, 

 Becquerel, and others, also touched the discovery. 

 These fragmentary gleams excited a momentary curi- 

 osity and were almost forgotten, when Faraday inde- 

 pendently alighted on the same facts; and, instead of 

 stopping, made them the inlets to a new and vast re- 

 gion of research. The value of a discovery is to be 

 measured by the intellectual action it calls forth; and 



* A letter addressed to me by Professor Weber on March 

 18 last contains the following reference to the connection here 

 mentioned : ' Die Hoffnung einer solchen Combination ist durch 

 Faraday's Entdeckung der Drehung der Polarisationsebene durch 

 inagnetische Directionskraft zuerst, und sodann durch die Ueber- 

 einstitnmung derjenigen Geschwindigkeit, welche das Verh&ltniss 

 derelectro-dynarnischen Einbeit zur electro-Ftatisclien ausdruckt, 

 mit der Geschwindigkeit des Lichts angeregt wnrden ; und mir 

 scheint von alien Versuchen, welche zur Verwirklichung dieser 

 Hoffnung gemacht worden sind, das von Herrn Maxwell gemachte 

 am erfolgreichsten.' 



