S44 ANNUAL REGISTER, 1794. 



transcendantly pure and inconceiv- 

 ably bright the rays of the sun are, 

 "when compared to the light of any 

 of our artificial illuminators, may be 

 gathered from the result of this ex- 

 periment. 



It appearing to me very probable, 

 that the difFercnce in the whiteness 

 of the two kinds of light, which 

 were the subjects of the foregoing 

 experiments, might, some how or 

 other, be the occasion of the diffe- 

 rent colours of the shadows, I at- 

 tempted to produce the same etfects 

 by employing two artificial li2;hts of 

 difterent colours ; and in this I suc- 

 ceeded completely. 



In a room previously darkened, 

 the light from two burning wax 

 candles being made to fall upon the 

 vhite paper at a proper angle, in 

 order to form two distinct shadows 

 of the cylinder, these shadows were 

 found not to be the least colour- 

 ed ; but upon interposing a pane of 

 yellow glass, approaching to a faint 

 orange colour, before one of the 

 candles, one of the shadows imme- 

 diately became yellow, and the other 

 blue. When two Argand's lamps 

 were made use of instead of the 

 candles, the result -was the same ; 

 the shadows were constantly and 

 very deeply coloured, the one yel- 

 low approaching to orange, and the 

 other blue approaching to green. 

 I imagined that the greenish cast of 

 this blue colour was owing either to 

 the want of whiteness of the one 

 light, or to the orange hue of the 

 other, which it acquired Irom the 

 glass. 



When equal panes of the same 

 yellow glass were interposed before 

 btiih the lights, the white paper 

 took an orange hue, but the shadows 

 were, to all appearance, without 

 the least tinge of colour j but tuo 



panes of the yellow glass ^being af- 

 terwards interposed befnre one of 

 the lights, while onlv one pane re- 

 mained before the other, the colours 

 of tlie shadows iranjcdi .tely re- 

 turned. 



The result of these experiments 

 havingconlirmed my suspicions, that 

 the colours of the shadows arose 

 from the dillerent degrees of white- 

 ness of the two lights, I now endea- 

 voured, by bringing day-light to be 

 of the same yellow tinge with can- 

 dle-light, by the interposition of 

 sheets of coloured glass, to prevent 

 the shadows being coloured when 

 day-light, and candle-light were to^ 

 gether the subjects of the experi- 

 ment ; and in this 1 succeeded. I 

 was e\ en able to reverse the colours 

 of the shadows, by causing the day- 

 light to be of a deeper yellow than 

 tlie cand'.e-light. In the course of 

 these experiments I observed that 

 difierent shades of yellow given to 

 the day-light produced very different 

 and often quite unexpected e<ft"ects : 

 thus one sheet of the yellow glass 

 interposed before the beam ot day- 

 light, changed the yellow shadow 

 to a lively violet colour, and the 

 blue shadow to a light green ; two 

 sheets of the same glass nearly de- 

 .stroycd the colours of both the sha- 

 dows ; and lliree sheets changed the 

 shadow w'hich was originally yellow 

 to blue, and that which was blue to 

 a purplish yellow colour. 



When the beam of day-light was 

 made to pass through a sheet of blue 

 glass, the colours of the shadows, 

 the yellow as well as the blue, were 

 improved and rendered in the high- 

 est degree clear and brilliant ; but 

 when the blue glnss was placed be- 

 fore the candle, the colours of the 

 shadows were very luuch impair- 

 ed. 



In 



