USEFUL PROJECTS. 



345 



In order to see what would be 

 the consequence of rendering the 

 candle light of a still deeper yellow, 

 1 interposed before it a sheet of 

 yellow or rather orange-colonred 

 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 suiface of the paper 

 appeared to be tinged of a most 

 beautihtl violet colour, approaching 

 to a light crimson or pink ; almost 

 exactly the same hue as I have often 

 observed the distant snowy moun- 

 tains and valleys of the Alps to take 

 aboiit 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, it is the white pa- 

 per illuminated by broad day-light, 

 and by the rays from a burning can- 

 dle, rendered still more yellow by 

 being transmitted through the yel- 

 low glass. The beautiful violet co- 

 lour 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 afi'ccted by it, 

 the other half of it remaining 

 white. 



To make these experiments with 

 moreconvcnience, the paper, which 

 may be about 8 or 10 inches .square, 

 should be pasted or glued down upon 

 a flat piece of board, furnished with 

 a ball and socket upon the hinder 

 side of it, and mounted upon a stand, 

 and the cylinder should be fastened 



to a small arm of wood, or of metal, 

 projecting forw ard from the boKom 

 of the board for that purpose. A. 

 small stand, capable of being liigher 

 or lower as the occasion requires, 

 should likewise be provided for sup- 

 porting the candle; and if the board 

 with the {Dnper fastened upon it be 

 surrounded with a broad black 

 fra.me, the experiments WjU be so 

 much the more striking and beauti- 

 ful. For still greater convenience, 

 1 have added two other stands for 

 holding the coloured glass through 

 which the light is occasionally made 

 to pass, in its way to the white sur- 

 face upon wiiich the shadows are 

 projected. It will be hardly ne- 

 cessary to add, that in order to the 

 experiments appearing to the great- 

 est advantage, all light, which is 

 not absolutely necessary to the ex- 

 periment, must be carefully shut 

 out 



Having fitted up a little appara- 

 tus according to the above direc- 

 tions, merely for the purpose of pro- 

 secuting these inquiries respecting 

 the coloured shadows, I proceeded 

 to make a great variety of experi- 

 ments, some with pointed views, 

 and others quite at random, and 

 merely in hopes of maiving some ae*- 

 cidcntal discovery that might lead 

 to a knowledge ot the causes of ap- 

 pearances which still sremcd to me 

 to be enveloped in much obscurity 

 and uncertainty. 



Having found that the shadows 

 corresponding to two like wax can- 

 dles were coloured, the one blue, 

 and the otheryellow, by inter|>osing 

 p sheet of jellow glass before one 

 of them ; I now tried what ■the ef- 

 fect would be u hen blue glass Vv'as 

 made Use of instead of yellow, and 

 I found it to be the same ; the .sha- 

 dows were still coloured, the one 



blue 



