490 Rev.W. V. Harcourt on Lord Brougham's statements 



down the principle that " the different volatility, or fixedness, 

 of the parts of bodies seems to consist only in this, that the 

 one is of a texture, or has component parts, which will be 

 easily rarefied into the form of air, and that the other hath 

 such as will not without much ado be brought to such a con- 

 stitution," Hook states that "in the dissolution of sulphureous 

 [combustible] bodies, by a substance inherent in, and mixed 

 with, the air, which is like, if not the very same with, that fixed 

 in saltpetre, a certain part of the bodies is united and mixed, 

 or dissolved and turned into, the air, and made to fly up and 

 down with it, in the same manner as a metalline or other body, 

 dissolved into any menstruum, doth follow the motions and 

 progress of that menstruum till it be precipitated." 



Even the fact, afterwards proved by Cavendish, of the den- 

 sity of the gaseous product of this dissolution, was predicted 

 by Hook ; for in an experiment — " to prove that the substance 

 of a candle or lamp is dissolved by the air, and the greatest 

 part thereof reduced into ajluid in the form of air," — he ob- 

 serves, that " the reason why this mixed body, which certainly 

 is otherwise heavier than the air, and so ought to descend, doth 

 notwithstanding ascend, is from the extraordinary rarefaction 

 of the same by the nearness and centrality of the flame and 

 heat, whereby it is made much lighter than the ambient 



air 



* » 



" * Experiment to prove that the substance of a candle or lamp is dis- 

 solved by the air, and the greatest part thereof reduced into a fluid in the 

 form of air — showed the Royal Society 22-29 Feb. 1671-2." — Registry of 

 the Royal Society. 



" Using a large reflecting glass, or convex refracting one, so placed in re- 

 spect to my eye that a candle, set at a certain distance beyond the refract- 

 ing glass, or between the eye and the surface of the reflecting glass, en- 

 lightened the whole area of the said glasses in respect to the eye, then con- 

 tinuing to keep the eye in that place where the area of the glasses 

 appeared to be wholly filled with the flame of the candle, I caused another 

 candle to be placed very near the said glasses, between the eye and the 

 glass, or beyond where I used the refracting glass, then looking steadfastly 

 at the flame of the last candle, it was very plain to be perceived, that the 

 flame thereof was encompassed with a stream of liquor, .which seemed to 

 issue out of the wick, and to ascend up in a continued current or jet d'eau, 

 and to keep itself entire and unmixed with the ambient air, notwithstanding 

 that it was a considerable way carried above the aforesaid flame. T was 

 yet further observable that the shining flame was placed in the midst of this 

 jet d'eau at the lower end thereof, but that it did not ascend proportionally 

 in height to the height of the jet d'eau, that where the tip of the flame 

 ended, there ascended up a small line of an opacousbody or smoke, which 

 to a good height above the flame kept the middle of the stream. The ma- 

 nifestation of these phaenomena was from the differing refraction of the 

 body of the jet d'eau from that of the ambient air, for the flame of the first 

 candle being but small and placed at considerable distance from the re- 

 fracting and reflecting globe, the smallest variation in the refraction of the 



