OF OPTICS. 



275 



round board A B C D E F G, and the outermost of LECT. 

 them divided into >^v-x. 



36U equal parts or 

 degrees : then, draw 

 seven right lines, as 

 A, B, &c. from 

 the center to the 

 outermost circle ; 

 making the lines 

 A and B in- 

 clude 80 degrees of 

 that circle ; the lines 

 B and C 40 

 degrees ; C and 



D 60 ; D and E 60 ; and F 48 ; 

 F and G 27; G and A 45. Then, be- 

 tween these two circles, paint the space A G red, in- 

 clining to orange near G; G .F orange, inclining to 

 yellow near F; FE yellow, inclining to green near 

 E; ED green, inclining to blue near D; DC blue, 

 inclining to indigo near C; CB indigo, inclining to 

 violet near B ; and B A violet, inclining to a soft red 

 near A. This done, paint all that part of the board 

 black which lies within the inner circle ; and putting an All the 

 axis through the center of the board, let it be turned J ^ 

 very swiftly round that axis, so that the rays proceeding bieml-d 

 from the above colours, may be all blended and mixed make"' 

 together in coming to the eye; and then, the whole white - 

 coloured part will appear like a white ring, a little 

 greyish ; not perfectly white, because no colours pre- 

 pared by art are perfect. 



Any of these colours, except red and violet, may be 

 made by mixing together the two contiguous prismatic 

 colours. Thus, yellow is made by mixing together a 

 due proportion of orange and green ; and green may 

 be made by a mixture of yellow and blue. 

 T 2 



