1835.] Accidental and Complementary Colours. 27 



which the solution is green by transmission as well as by 

 reflection, as may be seen if a test tube be filled with the 

 solution ; or, if a test glass, the shape of an inverted cone, 

 be employed, the light transmitted at and about an inch 

 above the apex will be green, and the ruby will gradually 

 appear as the eye is moved upwards towards the base, if I 

 may so speak. The transmitted light is also green, when 

 the solution is contained between two watch glasses placed 

 so as to form two convex surfaces. 



These observations apply also to the green solution 

 obtained by mingling muriatic acid and alcohol with a 

 boiling solution of chromate of potassa, in preparing the 

 hydrated oxide of chrome, and in either case the light may 

 be natural or artificial; indeed, the experiment is more 

 striking when flame is employed. 



The nitrate of chromium I find to be green by reflection 

 and transmission. 



Brown Street^ Salisbury^ Sth June, 1835. 



Article V. 



On the Number and Character of the Colours that enter into 

 the Composition of White Light. By P. C. 



Notwithstanding the present boasted state of Science, 

 and the numerous discoveries and improvements which 

 have undoubtedly been made, the whole of our arrange- 

 ments, with one solitary and splendid exception, the theory 

 of universal gravitation, are in a state of the greatest un- 

 certainty. There is scarcely a branch of science that does 

 not present us with at least two theories, the rival preten- 

 sions of which, though founded on different and even 

 opposite principles, it would be extremely difficult to decide. 

 The theory of chemistry, perhaps, thanks to the immortal 

 Lavoisier, for setting us free from the trammels of phlogiston, 

 is less chargeable with this defect than most others ; but 

 while one of its most important agents is treated in connexion 

 with another branch of science, by one party as the effect 

 of mere motion, and by another as a substantial body, and 

 chemistry leaves a question in which it is so deeply in- 

 terested , undecided ; it cannot be considered wholly divested 

 of uncertainty. It must be confessed, however, that the 



