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blue, indigo and violet is not yellow, the eye ought not to be in- 

 fenfible to this colour ; and confequently, fince by the exemption 

 of the yellow rays from the white folar light, that colour does 

 not refult, but a diflin<fi: purple, it follows, that the orange and 

 green are not primitive colours inherent in folar light. 



It remains now only for us to fhew, that the three colours of 

 red, yellow and blue are adequate to the folutlon of all the phae- 

 nomena of chromatics. But in order to fliew this, few words 

 will be fufficient, for having feen, that the feven prifmatic co- 

 lours can be generated by thefe three, it follows that all others 

 can be generated from them, as Sir I. Newton has proved at large. 

 However I think it will not be fuperfluous to obferve, that 

 white may be diredlly produced by thefe three colours, without 

 the previous generation of the other four prifmatic colours, in 

 the fame manner as it is ufually generated with feven. " I could . 

 " never yet," fays Newton, " by mixing only two primary co- 

 " lours, produce a perfecft white. Whether it may be compofed 

 " of a mixture of three, taken at equal diftances in the circum- 

 " ference, I do not know." Now to fhew that white may be 

 thus generated, let an annulus of about four inches diameter be 

 divided into three parts by lines tending towards the centre, and 

 let thefe three divilions be refpedlively painted red, yellow and 

 blue, in proportions to be afcertained by trial ; then if the 

 annulus be turned fwiftly round its centre, it will appear white. 

 That white may be generated by the mixture of only the three 



colours 



