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38 Doctor Tenxey, on Pr'mmd IcJc CoImu'S. 



tliat " to natural effects of tlie same kind, we arc, as far as 

 may be, to assign tlie same causes." Let us first examine 

 the doctrine by these rules. 



Three of the prismatiek colours we may every day, see pro- 

 duced by composition. Orange is evidently composed of red 

 and yellow ; green, of yellow and blue ; and purple, of blue 

 and violet. Nature, in the vegetable kingdom, is continu- 



ally producing and destroying them. Unripe oranges are 

 green J as they ripen, the blue particles give place to red; 

 which, with the more fixed yellow, form the colour dcnom- 

 inated from the fruit. The green colour of many plants is 

 changed, as they decay, into some of the shades of yellow, by 

 the escape of those particles which reflect blue rays. And 

 almost every body knows, that cloths are coloured green, by 

 being dipped successively in blue and yellow dies. Purple 

 may, in like manner, be produced by a mixture of blue and 

 violet liquors or powders. 



Now, is it consistent with the above cited rules to admit 

 orange, green, and purple to be compound colours in all ter- 



bodies; and at the same time to assert, 



J 



simple and oj^iginal in the rays of light ? Is it not rather totally 

 repugnant to them both? Further, writers on the su 



y 



allow, that all natural colours, not excepting white, may be 

 imitated by a mixture of proper proportions of red, yellow, 

 blue, and violet. Whence then, arises the necessity of admit- 

 ting three others to exist in light? But, if orange, green, and 

 purple be really original colours, inherent in the rays of 

 light, how does it happen, that these alone are capable of 

 being imitated by composition ? On Sir Isaac's theory, these 



queries 



