24-6 



Notes 



transmitted or reflected light of the particular colour wanted. 

 As candles and lamps are always at hand and solar rays not so, 

 I will here briefly describe the method of shewing any one, 

 and, consequently, all, of these beautiful experiments by candle- 

 light. 



7. L, M, N, o [in Fig. 27] is a piece of white paper, illum- 

 ined as in the figure ; d is a small cylinder of wood, as a black 



A smaU #A| A 



taper burn- ■^'^>^*Sf;^ 

 ing clear 



Fig. 27. 



lead pencil, or even one's finger, in such a manner as to pro- 

 duce the respective shadows d v and D K; c being a piece 

 of red glass in this experiment. 



8. If, instead of red glass, a piece of green glass be placed at 

 c, then the shadow d v will no longer be green, but of a red- 

 dish cast ; and so of the rest as mentioned above, at section 3. 



9. My friend was very desirous that I should endeavour 

 to account for these beautiful and most extraordinary appear- 

 ances ; with this view, I first observe that the burning lights, 

 A and B, when the experiments are made without daylight, may 

 be reckoned nearly white, particularly if they are made to burn 

 without smoke, though, in reality, they are yellowish, or even 

 orange-coloured sometimes, as is very plain when they are 

 compared with strong daylight. 



10. Secondly, white light is well known to consist of sev- 

 eral other colours, as red, orange, yellow, green, blue, purple, 



