On the Inflexion, Reflvxisii, and C'hurj of Light. 587 



tion for bodies, the violet the weakeft ; when therefore the gas and tlie body combine, the 

 precipitation of light muft be in the reverfe order of the affinity between the particles of light 

 and thofe of the bodies. If then the combin.ition talie place (lowly, the violet and blue par- 

 ticles will be firrt emitted, and laft of all the red : and this is confiftent with fail ; for any 

 inflammable body whatever, on being lighted, burns at firfl; with a blue or violet flame, and 

 afterwards has its flame of two or three diftincl colours, blue, white, red, &c. as is feen re- 

 markably in the cafe of a candle. Nay, 1 have obferved in the flame of a blow-pipe, all the 

 feven primary colours at once. When indeed a body is burnt in pure oxygenous gas, the 

 combination is fo rapid, that white light alone is precipitated undecompofed ; but in com- 

 mon air, where the azotic gas impedes the combullion, the above phenomena are obvious. 



4. A curious phenomenon has often furprifed philolophers, namely, blue Ihadovvs. Thefc 

 I have obferved at all times when the paper on which I received them was illuminated by the 

 flcy and any other light; and thereafon of them I take to be this: that the (liadow made by one 

 light is illuminated by the blue rays from the flcy -, fori have often obferved purple, and 

 even reddiflr ones, when the Iky or clouds Iiappened to be of ihofe colours; and this account 

 of the matter is confirnied by an experiment. Having received the coloured fpedlrum 

 made by a prifm with a large refrafting angle, on a fheet of rough wliitc paper, and held 

 above it another flieet ; I (lopped all the rays that illuminated the firil, except the blue, and 

 violet, and red; and if I held a body between the blue and the fecond paper, its (liadow was 

 red ; and if I held a body between the red and the paper, its (liadow was blue ; and fo of 

 other colours. This I take to amount to a demouftration of the thing *. 



5. Pa(ring over other phenomena of lefs note, I come now to one that has divided op- 

 ticians more than any other ; 1 mean the coloured fringes that furround the (liadows of 

 bodies. I made feveral obfervations 011 thefe, which enable me to conclude that each fringe 

 is an image of the luminous body ; for, holding between my eye and a candle two knife- 

 blades, as I approached the one to the other, the edge of the candle feemed multiplied, and 

 foon became coloured, coming wholly away from the candle ; and, as the knives approached 

 ftill nearer, became di(lin6l dilated images, highly tinclured with the prifmatic colours 5 

 and jurt: before the knives met, the candle, wliofe edges had been all along coloured 

 with red and yellow, became much dillended, till at lall it was divided in the middle, one 

 half feeming to be drawn away by each knife, and then it wholly difappeared. I have ob- 

 ferved three kinds of thefe images, two without, and one within the (liadow : the (ir!l had 

 its colours in the order from tlie (badow, red outermoil, and violet innermoft ; the fecond 

 and third had the colours in the contrary order; but the fecond was fo very f.iiiit that I could 

 never perceive it, unlcfs when let fall on my eye. All this iseafily explained by the diflcrent 

 flexibility of the rays. In (ig. 9, 1'late XXIII. let AD be a body by which the rays SDT and 

 S'D'T' pafs, and let SD be within AD's fphcrc of inflc^ion, and S'D'witliin its fphcrc of de- 

 flexion ; then SU will be bent into DG : but becaufe of the different inflexibility of its parts, 

 the red will be bent into DR, and the violet into 1)V, and the intermediate rays will fal} 

 between R and V; the whole forming an image RGV, feparatcd into the feven primary 



• Sine* wriring fhe above, I find the fame cxplaoatiop of ihe matter ^iyen by Mr. Milvill and foiiicof ihr 

 French acailtinicians, particulaily Meffis. Buffon and Bigudiii i alfoCount Rumford (I'liiloC Journal 1. 101 } , 

 fciii I have ilioujjlit fit to keep it in, on .iccoani of the c!c|icrinitnt iliai occurjcd 10 me in jllollraiii.n of it. 



4 F 2 colours ; 



