MEMOIR ON COLOURED SHAPOWS. 27 



The experiments were made in a dark room, every part Precautions »n 

 of which was painted black, for the purpofe of deftroying the ^^^^^JJJ.S^^^J'^ ex- 

 cplour produced by refle6led light. 



We at firfl illuminated the pafteboard by the light obtained Shadows from 

 from the corabuftion t)f fifli-oil in a common lamp, and by the ^jfj^^^en gas and 

 light of hidrogen gas, produced by the diflblution of zinc in 

 fulphuric acid weakened with water. The (badow produced 

 J)y intercepting the light of the hidrogen gas, was reddifh ; 

 that ariting from intercepting the light of the lamp, was bluiih. 



At the beginning we only ufed a feeble light from the hidro- 

 gen gas. Being fearful that the colour of the fliadows might 

 be occaiioned by the weak light, we filled a bladder with the 

 gas, and by compreffing the bladder ftrongly, produced a 

 powerful bright light : the plane illuminated by this light and 

 that of the lamp, afforded a fimilar refult ; the fiiadow from 

 the hidrogen gas was reddifli, that from the lamp bluifli. 



Qn enlightening the pafteboard by the light of a lamp and from a lamp and 

 that of alcohol, the interception of the light of alcohol pro-^'^°^°^> 

 duced a reddiih fliadow, and that of the lamp a bluifli fliadow. 



By illuminating it with the light of the lamp and that of a from a lamp and 

 candle, the (hadow from the candle was black, with a light- ^ '^^'^^^i 

 reddifli tinge ; that of the lamp was black, with a light-bluifli 

 tinge^ 



The pafteboard being illuminated with the light of a lamp from a lamp and 

 and that of a taper, the ftiadow from the taper was black flightly ^ ^T?^^* 

 reddened, and that of the lamp, black a little bluifti. 



The pafteboard illuminated, at the fame time, by the light from a lamp and 

 of a lamp and that from the combuftion of wood, the fhadow ^°° ' 

 thrown by the light of the wood was a violaceous blue ; that 

 of the lamp a reddifli yellow. 



The experiment was tried with wood burning with difficulty. In different 

 and producing little flame; with very dry wood producing ^^^"* 

 much flame; with chips of wood producing a white flame, 

 which reddened that of the lamp. When the furface was 

 enlightened with lights of equal intenfity, the coloured fliadows 

 offered little variation ; that proceeding from the light of the 

 wood was violaceous blue, that of the lamp reddifli yellow. 



The firft experiment was repeated in glafs-houfes where The experiment 

 wood is burnt. However bright the flame might be which '^JP^^^^'* '" * 

 was emitted through the working flues, the fliadow produced where wood is 

 by it on a furface alfo illuminated by the light of a lamp, was a ^"'""fj 

 violaceous blue, while that from the lamp was reddifli yellow. 



On 



