hy means of ordinary Artificial Light. 181 



E, horizontal line of flames parallel to the middle of A B, 

 and about half the height of A B, behind it, to diffuse the 

 light. It has already been remarked that gas is the most 

 suitable light, and that candles are the least so. 



F G, openings across the box, for the admission and dis- 

 charge of air, blackened within, and formed so that light 

 may not escape. 



H I, blue glass across the upper half of the box and a 

 little back from the front, so that the inequalities of the 

 paint on the glass may not appear on the front paper. 



I K, plies of tissue, or other white paper, immediately be- 

 low the glass, to reduce the light there to the same intensity 

 as that transmitted through the glass. 



I L, thin horizontal partition, almost touching the front 

 paper, to keep the two lights separate. 



White papers, moveable, are stretched across the front 

 AB, having colours or sketches painted upon them to shew 

 the contrast of the two lights, the upper half of the papers 

 exhibiting white light, the lower half ordinary artificial light. 

 The papers ought not to be thinner than " thin post." It is 

 better that they should be thicker if the light be sufficiently 

 strong. 



One paper which I shall exhibit, has vertical stripes of 

 white, and of the primary and the secondary colours, which 

 I painted by daylight with transparent water-colours, each 

 stripe of colour being light upon one side and gradually 

 deepening moderately to the other side. 



On looking at those stripes, and keeping in view that 

 white light gives the natural appearance of colours as in 

 pure daylight, it will be observed, that, by ordinary artificial 

 light, all is involved in the exceedingly strong orange tinge 

 before described, and the appearance of the colours is altered 

 accordingly; for example, white and yellow become hardly 

 distinguishable from each other. Orangey if pale, becomes 

 not distinguishable from yellow. If more intense, it becomes 

 a little warmer. Bed, if pale, becomes hardly distinguish- 

 able from yellow. If more intense, it becomes less or more 

 orange, and ultimately verges toward red. Blue, if of a cer- 

 tain intensity, becomes a pure neutral grey, the blue being 



