CONTRIBUTIONS TO SCIENCE. 



469 



Maxwell's first published experiments on the mixture of 

 coloured lights, executed while he was a B.A. at Cambridge, 

 had reference to the mixtures of coloured lights obtained 

 from coloured papers. One of the best accounts of these 

 experiments will be found in the paper read before the 

 Koyal Society of Edinburgh by Clerk Maxwell on 19th 

 March 1855. The instrument first employed was a top, 

 constructed by Maxwell himself; but he afterwards had tops 



Fig. 1. 



made by Mr. Bryson of Edinburgh. The coloured papers 

 were cut into circular discs, with a small hole in the centre 

 to admit the spindle of the top, and were slit along a radius 

 from the circumference to the central hole. By this means 

 two or more discs could be placed together, and by turning 

 one relatively to the others, more or less of any particular 



