42 Doctor Tenney, on Prismatich Colours. 



coiil<l proclnce no change in it: but, if it be a compound, 

 tills second operation, by separating the red from the yellow 

 rays, would annihilate it. But, on tlie former hypothesis, 

 that some red, and some yellow rays may be equally refran- 

 gible, this experiment _ would be indecisive; because no sepa- 

 ration would be effected by it. I think of one experiment, 

 by which (if it be practicable) some light may be thrown 

 on the subject, though perhaps, not sufficient to discover 

 where the truth lies. This is, to place four prisms in such 

 situations, that the red rays of one, and the yellow of an- 

 other, may be thrown together by the other two. If the 

 common prismatick orange should be thus produced, it would 

 be a strong circumstance in favour of my hypothesis. 



As I have no prisms within my reach, to make these, or 

 any other experiments, relative to the subject, it is not in my 



power. As I wish to have my ideas either verified or dis- 

 proved, if you have among your acquaintance any one, who, 



being possessed of the necessary apparatus, will take the 

 trouble of making some few such experiments, as the hints 

 I have given, or his own ingenuity, may suggest, you will 

 oblige me by turning his attention to the subject. And 

 should you judge this epistolary essay to be worthy of the 

 notice of the American Academy of. Arts and Sciences, I beg 

 you will do me the honour to present it. 



I am, my dear Sir, 



wii^h every sentiment of esteem, 



your most devoted, 



and humble Servant, 



The Eev. Mr. Belknap 



SAMUEL TENNEY 



11. An 



