Lesson xxv.] LIGHT AND COLOURS. 161 



Thus you have the regular gradations from one 

 Colour to another laid before you, agreeably to the 

 hypothesis which supposes the number of primary 

 Colours to be seven : but it is yet a matter of dis- 

 pute whether there are seven primary Colours, 

 or whether their number is greater or less than 

 s'even. Many persons assert that there are but 

 three primary Colours; but it is very evident that 

 they affix an idea to the term totally different from 

 that which is derived from Newton's definition. 

 He calls the Light whose rays are all alike refran- 

 gible, simple, homogeneal, and primary ; and he 

 shews that Colours may le produced by composi- 

 tion, which shall le light to the Colours of homo- 

 geneal Light, as to the appearance of Colour, but 

 not as to the immutability of Colour and constitu- 

 tion of Light. But the new opinion of the the- 

 orists above spoken of is, that the primary Co- 

 lours are red, yellow, and Hue, because, of pro- 

 per mixtures of these three Colours, all others 

 may be formed. It would be a needless multi- 

 plication of words to shew, that Newton and 

 they considered the subject in different points of 

 view. 



To have a familiar notion of the production of 

 Colours, let the following experiment be tried : 

 any time when the sun shines, standing in the 

 open air, let the bowl of a tobacco pipe be filled 

 with a lather of soap and water; then, gently 

 blowing at the other end, a large bubble will arise, 

 which let remain suspended at the top of the bowl: 

 then let two or three persons carefully observe the 



different 



