\l± CONSIDERATIONS OV COLOURS. 



bcctufe orange The explanation of thefe inftances by the rule propofed is 

 x-Tf ftttfckle. ^*^ 7 ' & we foPF^* ^ e wangc-colour of the little Grip to be 

 compounded of all the rays except blue, which is commonly 

 the cafe. 



A multitude of combinations of colours thus placed upon 

 one another, bring out toe colour of contrail indicated by the 

 O-mtnft motf- rule above laid down ; but there are feveral circumftances 

 ficd by ciicum- lnat refJ der (he effed more fir iking, or modify the refult. 

 Degreeof light. Sometimes it depends on the degree of light by which the 

 colours are obferved. They may be illumined uniformly, or 

 fome more than others. The quantity of light entering fimul- 

 taneoufly into the eye from ihe whole field of view, has like- 

 Many contraftj wife its influence. £f die colours form feveral furrounding 

 at once borders to each other, as a fcries of circles decreating.in tize 



and placed one upon another would do, they will act reci- 

 procally on each other. At every junction there will be on 

 each fide a border coloured by tfie contrail of the adjacent 

 tint, Thefe borders will be of greater or iefs extent in 

 proportion to the brigfatnefs of the colour. The effect, of a 

 single one may be fuSicient to deaden or annihilate all the 

 reft. 

 EH'e& increased The colours of contraft will appear like wife with greater 

 by Bight fatigue yjyjdnek aft^ having obferved them a few moments, or if the 

 coloured fubftances be ihaken a little, io that they may pafs 

 tlowly over the retina. It feems as if a certain fatigue of the 

 eye, either inftantaneoufly with regard to the intensity of the 

 light, or more (lowly by a prolonged vifion, concurred to 

 But not by ex- produce the appearances in queftion. But an exceflive fatigue 

 t&mct of the organ would produce a degeneration of the colours be- 



longing to another mode. 

 ColoaronAe We ought not therefore to refer to contraft thofe impref- 

 rcrma afterex- ^ ons , nen tioned by Jipinus, which are propagated in the eye 

 light, netfroxa with a certain duration, and a particular period or tints, when 

 cootraft. we nave footed ftedfaftly on a very brilliant light, as that of 



the fun. 

 Bufibn'cacel- But the colours termed by HufTmi accidental, on which 

 dental colours ut Scherfer has written an interefting efiay, belong to the clafs of 



contrafts, or at lead conftantly obferve the fame law. 

 toVnwed feaiows Coloured Jhadows are another phenomenon of the fame kind, 

 •f the Awe «a- Count Rumford has eftabliOied this fa& beyond queftion in 



