'3 7 6 Of the Propagation of Heat 



and that the fact which they prove would not have been 

 believed. 



That gunpowder may be inflamed, it is necessary that 

 the sulphur which constitutes one of its component parts 

 should be first melted and then boiled ; for it is the va- 

 pour of boiling sulphur which always takes fire when 

 gunpowder is kindled. 



Were melted sulphur a conductor of Heat, there is 

 reason to think that gunpowder would be very far from 

 being so inflammable as we find it to be. 



As those who have not been much accustomed to 

 meditate on the subject under consideration may find 

 some difficulty in conceiving how it is possible for in- 

 tense Heat to be excited in or to exist in the midst of a 

 mass of any cold liquid, as of water, for instance, 

 without immediately producing visible effects, I feel it to 

 be my duty to put that matter in the clearest light possi- 

 ble, and to show that what I have considered as being prob- 

 able is most undoubtedly very far from being impossible. 



The best method of proceeding in inquiries of this 

 kind, where the principal object is to discover whether a 

 supposed event, which, from its nature, cannot fall under 

 the cognizance of our senses, is or is not possible, seems 

 to me to be, to begin by supposing the event to have 

 actually taken place, and then to trace its necessary conse- 

 quences, and compare them with those appearances which 

 are actually found to take place. 



Adopting this method, we will suppose a quantity of 

 pure water, at the mean temperature of the atmosphere 

 in England, that of 55 F., to be put into a clean and 

 very transparent glass tumbler, placed in a window and 

 exposed to the direct rays of the sun. If the glass and 

 the water are both perfectly transparent^ it is evident that 



