!6 PIONEERS OF SCIENCE IN AMERICA. 



the solid parts of the blood, and that produced by the disten- 

 tion and contraction of the arteries, the resultant heat from 

 which is communicated to the blood. To account for the cold, 

 he supposed the blood to become so viscid that it could not pass 

 through the minute vessels at the extremities through which it 

 flowed freely when duly fluid ; hence, it bringing no more heat 

 to them, they grow cold. 



Franklin's views concerning the nature of fire and of heat 

 in general appear to have been partly in harmony with the 

 theory of phlogiston then current, and partly a vague concep- 

 tion of the undulatory theory, with its ethereal medium. They 

 are further given in a letter written to Benjamin Vaughn, in 

 1784, in which he said that he had long been of the opinion that 

 fire exists everywhere as in the state of a subtle fluid ; that too 

 much of the fluid in our flesh gives us the sensation we call 

 heat ; too little, cold ; its vibrations, light ; that all solid and 

 fluid substances which are inflammable have been composed of 

 it; their dissolution in returning to their original fluid state 

 we call fire. This subtle fluid is attracted by plants and ani- 

 mals in their growth, and consolidated ; is attracted by other 

 substances, thermometers, etc., variously ; has a particular 

 affinity with water, and will quit many other bodies to attach 

 itself to water, and go off with it in evaporation. 



To David Rittenhouse thus he wrote, in the same year, that 

 universal space, as far as we know of it, seems to be filled with 

 a subtle fluid, whose motion or vibration is called light. This 

 fluid may possibly be the same with that which, being attracted 

 by and entering into other more solid matter, dilates the sub- 

 stance by separating the constituent particles, and so rendering 

 some solids fluid and maintaining the fluidity of others. 



Franklin's speculations as to the origin of the globe are given 

 in a letter to the Abbe Sonleire, which was read as a paper 

 before the American Philosophical Society, September 22, 1782. 

 In it he supposes that all the elements in separable particles 

 being originally mixed in confusion and occupying a great 

 space, they would (as soon as the Almighty fiat ordained gravity, 

 or the mutual attraction of certain parts and the mutual repul- 

 sion of others, to exist) all move to their common centre; and 

 the air being a fluid whose parts repel each other, though drawn 

 to the common centre by this gravity, would be densest to- 

 ward the centre and rarer as more remote ; consequently all 



