Doctor Tenney, on Prmialick Colours. 



39 



queries do not appear to me to admit of a satisfactory solu' 



I 



tion. 



To this reasoning, it may probably be 



enquir 



of this kind, theory, ho 



d 



plausible, must ever 



give way to experiment. The prism actually separates a pencil 



of rays of li 

 fore, exist in 



distinct 



they must 



To this I would reply, that we ought not 



h 



suffer ourselves to be deceived by appearances 



In chem 



ical decompositions, we know, that most of the substances 

 obtained are themselves compounded ; and ma}; 

 other process, be again separated 



an- 



into 



mor 



simr 



. by 



le bodies. 



Why may not this be true of some of the colours, produced 

 by the prismatick decomposition of light ? In fact, I strongly 

 suspect a fallacy in the experiment, which has given rise 



r 



to a false deduction. Did either of the three colours, which 

 we find to be producible by composition, hold the first, or 

 the last place in the prismatick series; or, were any two of 

 them found 'together, no further proof of their simplicity 



could rea 



app'ear precisely in the places, which they ought to possess 



onably be demanded. But instead of this, they 



on the supposition of their being compounded 



Orang 



IS 



found between red and yellow;' green, between yellow and 

 blue ; and purple, between blue and violet. 



The existen 

 simple and 



of all the colours discovered by the prism 



depends entirely 



th 



truth of 



, M 



postulatum, which I apprehend has never been fully estab 



lished, viz. that the p 



effects a comj 



separ 



of 



b 



the different coloured rays. For if the separation 



perfect, intermediate colours must be produced. Now, can 



• it 



