204 Experimental Philosophy. [Lecture 14. 



To show further in what manner white is 

 produced. Let two circles be drawn, as in fig. 

 79, on a smooth round board ABCDEFG, and 

 the outermost of them divided into three hundred 

 and sixty equal parts or degrees : then draw seven 

 right lines, as A, B, &c. from the centre to the 

 outermost circle; making the lines A and B 

 include eighty degrees of that circle; the lines 

 B and C forty degrees ; C and D sixty ; D and 

 E sixty ; E and F forty-eight ; F and G twenty- 

 seven; G and A forty-five. Then, between 

 these two circles, paint the space AG red, in- 

 clining to orange near G ; GF 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 BA violet, in- 

 clining 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 axis through 

 the centre of the board, let it be turned very 

 swiftly round that axis, so that the rays pro- 

 ceeding from the above colours may be all blended 

 and mixed together in coming to the eye; and 

 then the whole coloured part will appear like a 

 white ring, a little grayish ; not perfectly white, 

 because no colours prepared by art are perfect. 



Any of these colours, except red and violet, 

 may be made by mixing together the two con- 

 tiguous prismatic colours. Thus, yellow is made 

 by mixing together a due proportion of orange 



