PHYSICS, EIGHTEENTH CENT. ELECTRICITY. 315 



found that when an exhausted glass globe is rubbed by the hand, 

 a vivid light is produced ; also when two pieces of lump sugar are 

 rubbed together, and in many other cases. He still did not suspect 

 that electricity was the cause of the light, for in the case of the ex- 

 hausted globe he attributes the light to some peculiar quality of the 

 glass. At last it occurred to him that the excitation of electricity 

 explained the luminous appearance ; and he found that a large glass 

 tube attracted light bodies when rubbed, and also gave off sparks. 

 When the interior of the tube was exhausted, the luminous appearances 

 were increased, but the attractive power was less. The arrangement 



FIG. 153. HAWKSBEE' s ELECTRICAL MACHINE. 



represented in Fig. 153 was then fitted up by Hawksbee, for the pur- 

 pose of better studying these luminous appearances, and the reader 

 will hardly fail to recognize in it the prototype of the cylinder electric 

 machines that are seen in cabinets of scientific apparatus at the present 

 day. But the apparatus has some special adaptation for the purpose 

 Hawksbee first intended it. There are two glass cylinders, an inner 

 and an outer one, and these could be exhausted so that the luminous 

 appearances in a vacuum might be studied ; or they might be filled 

 with various media. The glass cylinders could also be made to rotate 

 separately or together. Hawksbee relates many experiments with this 

 apparatus, noticing sometimes differences in the appearances observed 

 when only one cylinder revolved, when both revolved in one direction 

 or in contrary directions, when one of the cylinders was rubbed, when 



