104 Nichols: Franklin's 



diamonds, a phenomenon which he supposed to be con- 

 nected in some way with electrification. Wall/ about 

 1670, observed the sparks from amber when rubbed 

 with wool and, what is remarkable, compared the noise 

 and light produced to that of thunder and lightning. 

 Newton^ also paid some attention to electrical phenom- 

 ena, and he was perhaps the first to observe electrostatic 

 attraction through a solid dielectric. In his " Optics " 

 he put forth the hypothesis of an elastic fluid emitted by 

 electrified bodies and capable of penetrating solids such 

 as glass. 



The most notable electrical discoveries of the seven- 

 teenth century were, however, due to Otto von Guericke, 

 the inventor of the air pump, whose experiments ex- 

 tended from 1670 to 1700. He made an electrical ma- 

 chine consisting of a globe of sulphur mounted on an 

 axle and rubbed with the hand. He discovered the 

 repulsion between charged bodies and found that bodies 

 could be electrified without contact by bringing them 

 into the field of a body previously charged. He de- 

 scribed the sound of the electric discharge and compared 

 the spark to the light emitted by sugar when pounded 

 in the dark.^ The close of the seventeenth century is 

 likewise notable as the period during which the members 



'Wall: Phil. Trans. 1670. 



* Newton: Phil. Trans. 1675. 



'Priestley: History of Electricity, Vol. I, Page 11. 



