Encyclopaedia; or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of . yellow, and orange, in fame thing happened when I removed die prifmout of the funs light, and looked through it upon thehole fliining by the liglit of the clouds beyond it. Andyet if die refraition of all die ra)s were equal ac-cording to one proportion of the fines of in-cidence and relraflion, as is vulgarly fuppofed therefraaed image ought to have appeared round, byt
Encyclopaedia; or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of . yellow, and orange, in fame thing happened when I removed die prifmout of the funs light, and looked through it upon thehole fliining by the liglit of the clouds beyond it. Andyet if die refraition of all die ra)s were equal ac-cording to one proportion of the fines of in-cidence and relraflion, as is vulgarly fuppofed therefraaed image ought to have appeared round, bythe matheni^itical demonflratiin abovementioned. Sothen by thefe two experiments it appears, that inequal incidences there is a confiderable inequality ofrelVaaions. For the difcovery cf this fundamennJ property oflight, which has opened the whole inyflery of co-lours, we fee our aulhor was not only beliolden to theexperiments themielve?, which many others had madebefore him, but alfo tc his ikill in geometry ; v/hichwas abfolutely neceifavy to determine what the figureof the relraaed ima:e ought to be uptii the old prin-ciple of an equal refraaion of all the rays; but ha-ying Plate CCCLIX FUJ. A A ^H. Jf Tart r. Light dif-ferentlyrefrangi-ble. CCCLX. O P T I ving tlius made the difcovery, he contrived the follow-ing experiment to prove it at light. In the middle oitwo thin boards DE (/f, (fig. 3.),!. make a round hole in each, at G, and g, a third partof an inch in diameter; and in the window iliut amuch larger hole lieing made, at F, to let into mydavkened chamber a large beam of the funs light, Iplaced a prifm, ABC, behind the Ihut in that beam,to refrafl it towards the oppofite wall; and clofe be-hind this prifm I rixed one of the boards DE, in fucha manner that the middle of the refrafled light mightpafs through the hole made in it at G, and the relt beintercepted by the board. Tlien at the diilance ofabout 12 feet from the firft board, I fixed the otherboard, c
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Keywords: ., bookcentury1700, bookdecade1790, bookidencyclopaedi, bookyear1798
