Researches in Electricity 105 



of the Italian Academy " del Cimento " began their 

 studies of electricity. Among other things they observed 

 the discharging power of flames afterwards rediscovered 

 by Franklin. 



The earliest investigations of the eighteenth century 

 were those of Hauksbee who studied the electric glow 

 in vacuo over mercury, a phenomenon first observed by 

 Picard in 1670, and noted the great difference between 

 the discharge in vacuo and that occurring at ordinary 

 pressures. Hauksbee made a machine having a revolving 

 globe of glass rubbed with the hand. 



After Hauksbee there was a lull in electrical interest 

 which lasted for a quarter of a century. Then came 

 the period of intense activity which culminated in Frank- 

 lin's work. The revival appears to have had its origin 

 in England about 1728, at which time Stephen Grey of 

 London began a remarkable series of experiments in 

 association with a friend, the Rev. Mr. Wheeler. They 

 found that such substances as hair, silk, linen, wool, 

 paper and leather could be electrified by friction and 

 discovered in 1729 the conduction of the charge from 

 an electrified body to neighboring bodies. In attempt- 

 ing to transmit the electrification along a linen thread 

 they found it necessary to insulate the line by means 

 of silk cords, and were thus led to a recognition of the 

 distinction between conductors and non-conductors. They 

 succeeded ultimately in transmitting the electric charge 



