480 SPECIAL METHODS OF DISCOVERY. 



Otto Gruericke, by means of his electric machine (com- 

 posed of a globe of sulphur and a piece of cloth, and 

 invented about the year 1672), increased our knowledge of 

 electricity in several ways ; he discovered electric repul- 

 sion, and also that light and sound accompanied strong 

 electrical action. Hawksbee made further discoveries in 

 the same science, by inventing and using, in the year 

 1709, a globe of glass for an electric machine. Boze, in 

 1741, first employed a prime conductor with the machine ; 

 Winkler, in the same year, first introduced the cushion as 

 a rubber ; and Gordon, in 1 742, first employed a glass 

 cylinder. In 1745, both Kleistand Muschenbroeck simul- 

 taneously invented the Ley den jar. In the following year 

 Cunseus independently invented it ; and many new effects 

 were obtained and discoveries made by its aid, because it 

 enabled the electric power to be collected in large amount. 

 Canton, about the year 1751, first coated the cushion 

 with an amalgam of tin, and discovered that it was 

 advantageous. By the use of his lightning-rod, M. 

 Dalibard, in the year 1752, discovered that electric 

 sparks could be obtained from the atmosphere, and in 

 the same year both Dr. Franklin and M. de Komas, by 

 means of their electric kites, collected electricity from 

 the clouds, and discovered that it was identical with 

 lightning. Volta, in the year 1776, invented the electro- 

 phorus, and discovered various new truths in electric 

 science, by its employment. Von Marum, about the 

 same year, employed a circular disc of shellac for an 

 electric machine. Although Eobison in 1769, and Mayer 

 also, had partly proved that electric attraction acts 

 with an intensity which varies inversely as the square 

 of the distance, it was Coulomb, by the use of his 

 torsion-balance and proof-plane, who discovered, about 

 the year 1785, how to measure very small quantities of 



