BENJAMIN FRANKLIN. ! 5 



anybody has hitherto considered. When put on water it spreads 

 many feet around, becoming so thin as to produce the prismatic 

 colours for a considerable space, and beyond them so much 

 thinner as to be invisible, except as to its effect in smoothing 

 the waves at a much greater distance. It seems as if a mutual 

 repulsion between its particles took place as soon as it touched 

 the water, and a repulsion so strong as to act on other bodies 

 swimming on the surface, . . . forcing them to recede every 

 way from the drop as from a centre, leaving a large clear space. 

 The quantity of this force, and the distance to which it will 

 operate, I have not yet ascertained ; but I think it is a curious 

 inquiry, and I wish to understand whence it arises." The con- 

 tinued study of this subject has given rise to many curious 

 observations, and has thrown considerable light on the prop- 

 erty of surface tension of liquids. 



The nature of inflammable and uninflammable gases was not 

 yet understood, although Priestley was engaged, with his co- 

 workers, in Europe, in the experiments by which it was finally 

 elucidated; and to him Franklin wrote, in 1774, as a contribu- 

 tion to the list of phenomena to be accounted for, concerning a 

 river in New Jersey, that on stirring the bottom bubbles arose 

 which could be set on fire ; and he related an experiment made 

 upon this river by the Rev. Dr. Finley, president of the college 

 at Princeton. "The discoveries," he added, "you have lately 

 made of the manner in which inflammable air is in some cases 

 produced, may throw light on this experiment, and explain its 

 succeeding in some cases and not in others." In another letter 

 to Priestley, Franklin illustrated the pleasant relations he en- 

 joyed with that philosopher, and manifests his sympathy with 

 his work by saying : " I find that you have set all the philoso- 

 phers of Europe at work upon fixed air ; and it is with great 

 pleasure that I observe how high you stand in their opinion, 

 for I enjoy my friends' fame as my own." 



How far Franklin and the world were still, however, from 

 understanding the true nature of chemical heat-producing 

 processes, is shown in a curious speculation in his hand- 

 writing found among the papers of Cadwallader Golden, in 

 which the heat of the blood and the cold and hot fits of some 

 fevers were explained by supposing that the heat is a matter of 

 friction, not of the liquid blood, for liquids have no friction, 

 and water cannot be warmed by shaking it, but by friction of 



