6 THE ELECTRIC TELEGRAPH. 



at the expense of much, pains, arranged and published a 

 list of all those bodies in which he had observed the same 

 property. 



Towards the middle of the seventeenth century Dr. Wall 

 discovered the electric spark on rubbing a cylinder of amber 

 with a piece of flannel. On approaching the cylinder with 

 his linger, he obtained, for the first time, the spark, and 

 noticed the noise which always accompanies it. 



Boyle and Otto Guericke added to the little stock of know- 

 ledge then in hand, as well as Hawkesbee ; but their dis- 

 coveries are a little out of the reach of Telegraphy. 



3. The first discovery which we have on record of the 

 power of transmitting the electric fluid to a distance through 

 an insulated wire, is that of Stephen Grey, pensioner of the 

 Charter House. Grey, having succeeded in electrifying a 

 glass tube open at both ends, was desirous of finding out 

 whether he could obtain the same result if he stopped up the 

 ends with corks. This shows how at random the experi- 

 ments were conducted at that date, and how little system had 

 been introduced into these inquiries. But Grey's experiment 

 succeeded, and he was surprised to find the corks also highly 

 electrified. On presenting the corked ends of the tube to a 

 feather, he found that the feather was first attracted and then 

 repelled. This led him to infer that the electricity which the 

 tube had acquired by friction passed spontaneously to the 

 corks. From the communication of electricity from tubes to 

 corks Grey was led to transmit it through strings and 

 wires; and in 1727 we find him employing a wire 700 feet 

 long, suspended in the air by silk threads, to one end of 

 which he brought his excited glass tube, whilst another 

 person at the other end observed the electrification. 



4. After Grey, the subject was taken up by Desaguilliers, 

 who instituted inquiries into the different conductibilities 

 of bodies. The discoveries of Grey had caused the bodies 

 operated on to be assorted into two classes, which Desa- 

 guilliers proposed to distinguish by the names of "electrics" 

 or non-conductors, and " non- electrics " or conductors. 



5. On making experiments on the attraction of any light 



