prior to the Introduction of the Potentials. 43 



certain circumstances, it was possible to render the electricity in 

 some bodies more rare than it naturally is, and, by communi- 

 cating this to other bodies, to give them an additional quantity, 

 and make their electricity more dense." 



In the same year in which Watson's theory was proposed, a 

 certain Dr. Spence, who had lately arrived in America from 

 Scotland, was showing in Boston some electrical experiments. 

 Among his audience was a man who already at forty years of 

 age was recognized as one of the leading citizens of the English 

 colonies in America, Benjamin Franklin of Philadelphia (b. 1706, 

 d. 1790). Spence's experiments " were," writes Franklin,* 

 " imperfectly performed, as he was not very expert ; but, being 

 on a subject quite new to me, they equally surprised and 

 pleased me." Soon after this, the "Library Company" of 

 Philadelphia (an institution founded by Franklin himself) 

 received from Mr. Peter Collinson of London a present of a glass 

 tube, with some account of its use. In a letter written to 

 Collinson on July llth, 1747,f Franklin described experiments 

 made with this tube, and certain deductions which he had 

 drawn from them. 



If one person A, standing on wax so that electricity cannot 

 pass from him to the ground, rubs the tube, and if another 

 person B, likewise standing on wax, passes his knuckle along 

 near the glass so as to receive its electricity, then both A and B 

 will be capable of giving a spark to a third person C standing 

 on the floor; that is, they will be electrified. If, however, A 

 and B touch each other, either during or after the rubbing, they 

 will not be electrified. 



This observation suggested to Franklin the same hypothesis 

 that (unknown to him) had been propounded a few months 

 previously by Watson : namely, that electricity is an element 

 present in a certain proportion in all matter in its normal 

 condition ; so that, before the rubbing, each of the persons A, 

 B, and C has an equal share. The effect of the rubbing is to 



* Franklin's Autobiography. 



t Franklin's New Experiments and Observations on Electricity, letter ii. 



