64 MR. J. SMITH ON THE ORIGIN OF COLOUR 



I.— HOEIZONTAL MOTION. 



1st Class of Experiments. 



Coloured Reflection. Theory of light and shade by 



horizontal motion. 



96. If we take a piece of Bristol board [see plate IV. 

 fig. 3) in the form of the parallelogram A B, and examine 

 it carefullyj the light reflected from every spot, as far as 

 the eye can detect, is the same. The space surrounding 

 the card is all darker than the card, and may be consi- 

 dered as shadow. Perforate a hole in the centre 0, and 

 make it revolve on the centre, then the disc formed by 

 the revolution will not be of a uniform colour. There will 

 be a ring on the disc of a diflereut shade for every radius 

 that can be drawn from the centre of motion on the card. 

 The outer ring will have for its radius half the diagonal 

 A B, the next will have for its radius half the side AD ov 

 E 0, and the third will have for its radius half the end 

 D B, or F. The inner circle formed by the radius F, 

 equal to half the end, vdll be white, because there is no 

 mixture of shade during revolution, there is no interval in 

 the revolution of the ray; the next, or the circle formed 

 by the radius equal to half the side A D, will be coloured, 

 for here there is a mixture of light and shade, and the 

 outer circle will have a darker shade of colour, for there 

 is less light compared to the dark, as may be seen by in- 

 specting the diagram, By making the parellelogram, 

 therefore, revolve we get a variety of colour ; but colour is 

 only produced where there is light and darkness repeated 

 at intervals, a result not at all anticipated by science; a 

 result, however, quite in accordance with our course of 

 reasoning. 



97. If the parallelogram is made to revolve on the centre 

 0, the ratio of the black to the white is apparent to the eye 



