314 A SHORT HISTORY OF SCIENCE 



showing that light could be produced by passing common air 

 through mercury placed in a well-exhausted receiver. These 

 phenomena, which had been observed before Hawksbee's time 

 and had been variously explained, were attributed by him to 

 electricity, for he remarked their resemblance to lightning. Like 

 Newton he used a revolving glass globe, rubbed by the hand, to 

 generate electricity. These and other results he published in 

 1707-1709. 



Further investigations by Wall, Gray and Wheeler, Desagu- 

 liers, Dufay, and many others prepared the way for Watson, 

 Franklin, Galvani, and Volta, whose investigations in the latter 

 half of the eighteenth century, added to those just referred to, 

 would alone make that century forever famous in the history of 

 science. On these brilliant discoveries we can only briefly touch. 

 Wall (1708) compared the electric spark and its crackling to 

 lightning and thunder. Gray and Wheeler (1729) and later Dufay 

 created what has been called an epoch in the history of electricity 

 by discovering that different bodies differ in electrical conductiv- 

 ity, while Desaguliers confirmed and extended their results. 

 Dufay (1699-1739) repeated these and other experiments and 

 discovered that there are two kinds of electricity, positive and nega- 

 tive, or, as he called them from their source of origin, vitreous and 

 resinous. Watson undertook with the aid of a party of friends 

 from the Royal Society to determine the velocity of the electric 

 current and found " that through the whole length of a wire 12,276 

 feet long, the velocity of electricity was instantaneous." Many 

 others had also made important, if minor, contributions to the new 

 science of the electric "fluid" -for like heat (caloric) electricity 

 was regarded as material though imponderable before that 

 science was further developed and widely popularized by Frank- 

 lin. 



Benjamin Franklin (1706-1790) was not the first American to do 

 good work for science, but he was the first to gain wide renown 

 in it together with an international reputation. Even before 

 1750, Franklin had argued that all the known phenomena of elec- 

 tricity had their counterpart in lightning, but it was not until 



