428 Mr. Crace Calvert on [May 8, 



WEEKLY EVENING MEETING, 

 Friday, May 8. 

 The Lord Wensleydale, Vice-President, in the Chair. 

 F. Grace Calvert, Esq. F.C.S. M.R.A. Turin, 



HONOBABY PROFESSOR OF CHEMISTRY, ROTAI, INSTITUTION, MANCHESTER. 



On M. ChevreuVs Laws of Colour. 



Mr. Grace Calvert stated that he had three objects in view in 

 this discourse. The first was to make known the laws of colours, as 

 discovered by his learned master, M. Chevreul ; secondly, to explain 

 their importance in a scientific point of view ; and, thirdly, their 

 value to arts and manufactures. 



To understand the laws of colours, it is necessary to know the 

 composition of light ; Newton was the first person who gave to the 

 world any statement relative to the components of light, which he 

 said consisted of seven colours — red, orange, yellow, green, blue, 

 indigo, and violet. It is now distinctly proved that four of those 

 seven colours of the spectrum are the result of the combinations 

 of the three colours now known as the primitive colours, viz., red, 

 blue, and yellow. Thus blue and red combined produce purple or 

 indigo ; blue and yellow, green ; while red and yellow, produce 

 orange : these facts being known, it is easy to prove that there are 

 not seven, but three primitive, and four secondary, called com- 

 plementary colours. 



Several proofs can be given that light is composed of three 

 colours only. One of the most simple consists in placing pieces of 

 blue, red, and yellow papers on a circular disc, and rotating it 

 rapidly ; the effect to the eye being to produce a disc of white 

 light. If, therefore, the eye can be deceived so readily while the 

 disc travels at so slow a rate, what must necessarily be the case 

 when it is remembered that light proceeds at the rate of 190,000 

 miles per second ? 



The rapidity with which light travels is such that the eye is not 

 able to perceive either the blue, red, or yellow, the nerves of the 

 retina not being sensitive enough to receive and convey successively 

 to the mind the three or seven colours of which the light is com- 

 posed. 



Before entering into the laws of colour, Mr. Crace Calvert 

 stated that it might be interesting to know what scientific minds 

 had devoted attention to the laws of colours. 



