hi Fhdds. 391 



observed that the oil had become perfectly colourless, 

 and appeared to me to be nearly as transparent as the 

 purest water. On the approach of winter I found that 

 this oil was much more liable to be congealed with cold 

 than oil of the same kind which had stood near it many 

 months in a large glass bottle closed with a cork. 



§ 6. An unsuccessful Attempt to cause radiant Heat from a 

 red-hot Iron Bullet to descend in Oil. 



Having poured a quantity of this colourless oil into a 

 glass tumbler, and caused it to congeal throughout, I 

 presented to its upper surface a red-hot iron bullet, \\ 

 inches in diameter, and held it quite close to the oil sev- 

 eral minutes, till the bullet ceased to be red-hot. As the 

 oil seemed rather to be merely thickened by the cold, 

 and to have lost its transparency in consequence of the 

 presence of a number of opaque particles, which were 

 everywhere dispersed about in it, than to be congealed 

 into a solid mass, I thought that if it were possible for 

 radiant Heat to descend in any Fluid it might perhaps 

 be in this ; and if this should happen I was certain to 

 make the discovery by the manner in which the oil re- 

 covered its transparency ; for should radiant heat de- 

 scend, the form of the mass of oil first restored to its 

 transparency must necessarily have been hemispherical^ or 

 some section of a sphere, or at least of some convex 

 figure ; but the under part of that part of the oil which 

 was restored to its transparency in this experiment was, 

 to all appearance, as perfectly flat and horizontal as the 

 upper surface of it, which proves that the Heat, by 

 which the congealed oil was thawed, was communicated 

 to it, not immediately by the red-hot bullet, but me- 



