264 GREAT MEN OF SCIENCE 



means of a difficult experimental investigation, and found 

 to be identical with the velocity of light as known since 

 Roemer's time. Here for the first time the velocity of 

 light was found to play a decisive part in the domain of 

 purely electromagnetic phenomena, the velocity which is so 

 characteristic a magnitude for ether waves, that is, light. 

 It was legitimate to regard this as a definite sign of the cor- 

 rectness of Faraday's idea, that the electromagnetic forces 

 are states in space which have to do with the same ether as 

 that which carries light. This idea was later thoroughly 

 worked out by Maxwell, whose work rested in particular 

 upon Weber's researches. 



The velocity of light had also appeared in another con- 

 nection - also within the range of Weber's researches - as 

 a determining electrical quantity, namely as the velocity of 

 propagation of electric tension along telegraph wires. The 

 electromagnetic telegraph had been introduced by Gauss and 

 Weber in the year 1833,^ and had very soon spread further, 

 and this led to the velocity being measured by means of a 

 rotating mirror; it was found to be practically equal to the 

 velocity of light, which fact also became of importance as 

 regards conclusions to be drawn later. 



Weber was also the first who attempted to develop quite 



^ Telegraphy by means of light signals had already long been in exis- 

 tence. Ideas of, and attempts at, electric telegraphy were also fairly old; 

 very shortly after Gray had discovered the possibility of conducting 

 electricity to a distance, a * beginning was made with telegraphy, 

 and every newly discovered electrical effect - in particular the chemical 

 effects of the current - gave a new spur to plans of this kind, but 

 in every case it was supposed to be necessary to use almost as many 

 wires as there are letters in the alphabet, and hence no practical results 

 were obtained. Gauss and Weber were certainly the first to carry out 

 electric telegraphy with two wires only, for they signalled to one another 

 between the observatory and the physics institute in Gottingen by 

 means of the deflection of a magnet, the current being produced by in- 

 duction, so that no other source of current was necessary. Very shortly 

 afterwards (first in Bavaria), it was found out how to work with only one 

 wire, by using the earth as return for the current. Gauss and Weber abso- 

 lutely refused to attempt to gain any personal advantages for themselves 

 from the introduction of the electric telegraph. 



