VOL. LXXXIV.3 PHILOSOPHICAL TRANSACTIONS. 377 



rendered in the highest degree clear and brilliant; but when the blue glass was 

 placed before the candle, the colours of the shadows were very much impaired. 



In order to see what would be the consequence of rendering the candle light 

 of a still deeper yellow, I interposed before it a sheet of yellow or rather orange- 

 coloured glass, when a very unexpected and most beautiful appearance took 

 place; the colour of the yellow shadow was changed to orange, the blue shadow 

 remained unchanged, and the whole surface of the paper appeared to be tinged 

 of a most beautiful violet colour, approaching to alight crimson or pink; almost 

 exactly the same hue as I have often observed the distant snowy mountains and 

 valleys of the Alps to take about sunset. Is it not more than probable that this 

 hue is in both cases produced by nearly the same combinations of coloured light? 

 In the one case, it is the white snow illuminated at the same time by the purest 

 light of the heavens, and by the deep yellow rays from the west; and in the 

 other, the white paper illuminated by broad day light, and by the rays from a 

 burning candle, rendered still more yellow by being transmitted through the 

 yellow glass. The beautiful violet colour which spreads itself over the surface of 

 the paper will appear to the greatest advantage, if the pane of orange-coloured 

 glass be held in such a manner before the candle, that only a part of the paper, 

 half of it for instance, be affected by it, the other half of it remaining white. 



To make these experiments with more convenience, the paper, which may be 

 about 8 or 10 inches square, should be pasted or glued down on a flat piece of 

 board, furnished with a ball and socket on the hinder side of it, and mounted 

 on a stand; and the cylinder should be fastened to a small arm of wood, or of 

 metal, projecting forward from the bottom of the board for that purpose. A 

 small stand, capable of being made higher or lower as the occasion requires, 

 should also be provided for supporting the candle; and if the board with the 

 paper fastened on it be surrounded with a broad black frame, the experiments 

 will be so much the more striking and beautiful. For still greater convenience, I 

 have added 2 other stands, for holding the coloured glass through which the 

 light is occasionally made to pass, in its way to the .white surface on which the 

 shadows are projected. It will be hardly necessary to add, that in order to the 

 experiments appearing to the greatest advantage, all light, which is not absolutely 

 necessary to the experiment, must be carefully shut out. 



Having fitted up a little apparatus according to the above directions, merely 

 for the purpose of prosecuting these inquiries respecting the coloured shadows, 

 1 proceeded to make a great variety of experiments, some with pointed views, 

 and others quite at random, and merely in hopes of making some accidental dis- 

 covery that might lead to a knowledge of the causes of appearances which still 

 seemed to be enveloped in much obscurity and uncertainty. Having found that 

 the shadows corresponding to 2 like wax candles were coloured, the one blue, 



VOL. XVII. 3 C 



