the Light of Bodies in a State of Comhuftien. rgj 
upon any hard globular fubftance. Gradually bring the paper, 
thus formed, to that diftance from the candle at which it will be- 
gin to take fire. In this cafe a beautiful blue flame may be feen, 
hanging as it were by the paper till a hole is made in it, when 
the flame, owing to the mcreafed adlion of the air upon all 
parts of it, becomes white, though the edges flill continue of 
a blue or violet colour. As a confirmation of what I have 
concluded from the preceding faffs, it may be obferved, that 
the very flame which, when expofed to a certain degree of 
heat, emitted the moil refrangible rays only, will, if expofed 
to a greater degree of heat, emit fuch as are lefs refrangible. 
The flames of fulphur, fpirits of wine, &c. when fuddenly 
expofed to the heat of a reverberatory, change their blue ap- 
pearance for that which is perfeflly white. But to gain a 
more’ linking diverfity of this fa£l, I adopted Mr. Melvill’s 
mode of examining bodies whilft on fire. I darkened my 
room, and placed between my eye and the combuftible a fheet 
of pafteboard, in the center of which I 'made afmall perfora- 
tion. As the light of the burning body efcaped through this 
perforation, 1 examined it with a prifm, and obferved the fol- 
lowing appearances. When the fpirits of wine were let on 
fire, all the rays appeared in the perforation ; but the violet, 
the blue, and the green, in the greateft abundance. When 
the corribuAion of the fpirits was checked by throwing fome 
fal ammoniac into the mixture, the red rays difappeared ; but 
when, by the long continuance of the flame, the fal ammoniac 
was rendered fo hot as to increafe, rather than ditninifh the' 
eombuftioii, the red rays again appeared at the perforation. If 
the fcreen was managed fo that the different parts of the 
flame might be examined feparately, I always obferved that 
Vol® LXX¥. C c the 
