28 P. C. on the Colours that enter into the [July 



fault is chargeable rather upon its non-interference than its 

 want of power to decide.* 



It is not perhaps surprising that questions which require 

 for their determination the concurring evidence of various 

 classes of phenomenja, which at present form the basis of 

 distinct sciences, and a connexion between which is not 

 usually considered essential, should remain without satis- 

 factory answers ; but there are questions of minor import- 

 ance, the unsettled state of which has no such excuse to 

 offer; their solution requires only the arrangement and 

 combination of known and admitted facts ; and we can only 

 account for the state of uncertainty in which they have 

 been suffered to remain, upon the well known principle, 

 that whatever is constantly within our reach is frequently 

 neglected, while distant objects, which present greater dif- 

 ficulties without, perhaps, corresponding importance, are 

 pursued with avidity. 



Among questions of this description, the number and 

 character of the primitive coloured rays which enter into 

 the composition of white light, is one, the decision of which 

 is of considerable importance to the arts ; and we have, 

 therefore, the inducement of utility, in addition to more 

 speculative motives for its investigation. 



Sir Isaac Newton, the illustrious founder of the material 

 theory of light, divided the spectrum into seven colours ; 

 each of which he considered differed from the others in its 

 degree of refrangibility, but by such an imperceptible grada- 

 tion, that the most refrangible ray of one colour, approached 



* It has long been evident that the material character of light and heat must 

 stand or fall together : if there had been a doubt on this point, the recent dis- 

 coveries of Professor Forbes must have removed it. How then will the chemist, 

 the results of whose experiments have hitherto been satisfactorily accounted for, 

 by considering caloric a material and indestructible agent, reconcile the change 

 which must be the necessary consequence of adopting the undulatory theory of 

 light, so as to preserve the consistency of his explanations 1 Or rather, will he 

 not impose this impossible task upon the undulationist, as one of the conditions 

 upon which his theory ought to be received. 



The philosopher who does not confine his views to one branch of science, but 

 who looks upon the different phenomena of nature as a whole, which must ulti- 

 mately be connected in theory, as they are already united in operation, will 

 certainly not tolerate the retrogression which must be the necessary consequence 

 of adopting such opposite opinions respecting the same object when applied to 

 diflferent purposes. If heat be a material agent in chemistry, it must be a 

 matrial agent in those experiments which connect it with light. 



