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XL. Account of some Optical Experiments, By Samuel 

 Sharpe, Esq. F.G.S.* 



Expo: 1. — T HELD a card between my eye and the candle, 

 -*■ and moved it gradually till it very nearly hid 

 all the flame, when the edge of the card was tinged with red, 

 and the yellow and blue, &c. appeared in succession further 

 from the card. The order of the colours proves that the ray 

 of light is (at least principally) refracted round or towards, and 

 not Tiom, the edgef . 



Fig. 1. A is a section of the flame, 

 B of the eye, 



CD of the card ; 



and R Y V (using three, instead of the seven, for shortness) 

 are the prismatic rays. 



The red rays are in excess because of the colour of the 

 flame ; and when the card is moved still more towards V, the 

 red is no longer seen, the blue and violet are so pale as to be 

 hardly seen. 



By measurement which was not very accurate, the red rays 

 appeared to be refracted about 28'; and my measurement was 

 not accurate enough to determine whether or not different sub- 

 stances refracted light differently. The brightest rays appeared 

 071 the card rather than by the side of it, as in fig. 8, making 

 the fringe described in Experiment 5, and from the cause 

 there mentioned. Part of the inaccuracy of the measurement 

 mentioned above arose from this fringe. 



If I applied to the ray a second card B (fig. 9), between the 

 first card A and the candle, and in the same direction, the ray 

 disappeared, being refracted to C. 



If I applied it in the contrary direction, as D, no apparent 

 change took place, because, though one ray might be refracted 

 round D, there were others to fall on A; but when the second 

 card was ajiplied exactly opposite to A, as E, then the coloured 

 rays were gradually diawn towards E, as it approached. 



Exper. 2. — I held before my eye the eye-glass of a tele- 

 scope having parallel cobwebs in the focus, and moved it be- 

 fore the cantlle till the light fell obliquely on the cobwebs: the 

 cobweb at II (fig. 1.) was completely red ; and as I moved it 

 towards V, the cobwebs were prettily coloured with each of the 

 colours in its turn. 



• Commiinicatecl by tlic Author. 



+ Xcwtoii a()i)cars to contradict himself in liis Optics and Principia; in 

 one stating tliat light is refracted round or towards, and in the other /row, 

 an intervening edge. 



N. S, Vol. 7. No, 40. April 1830. 2 O This 



