REFRACTION. 



fine of the refralled angle, is fixed and conflant ; viz. if the 

 reflation be out of air into glafs, it is found greater than 

 as 1 14 to 76, but lefs than 115 to 76; that is, nearly as 

 3 tr, 2. 



This ratio, afligned by Huygens, agrees with another of 

 fir Kaac Newton, who makes the fine of the angle of in- 

 clination to the fine of the refrafted angle, as 3 1 to io ; 

 whicli is, likewife, nearly as 3 to 2. Indeed, there is fonic 

 diifereuce in the quantity of refradlion, in different kinds 

 of glafs; but in phyfical matters, precifenefs is not nccefl'ary. 

 In rain-water, Defcartcs found the ratio of the fine of 

 the angle of inclination, to the fine of the refrafted angle, 

 as 250 to 187, that is nearly as 4 to 3 ; which agrees with 

 fir Ifaac Newton's obfervation, who makes it as 529 to 396. 

 In fpirit of wine, the fame great author makes the ratio 

 as ICX3 to 75 ; which is not far from the fefquitertian ratio. 

 In air he makes it as 3201 to 3200; and as to air, he 

 {hews, that a ray of light, in traverfing quite through the 

 atmofphere, is rafrafted the fame as it would be, were it to 

 pafs with the fame obliquity out of a vacuum into air of equal 

 denfity with that in the lowefl; part of the atmofphere. 



See the following table, in which the proportion of the 

 fines which mcafure the refraftions of feveral bodies ; the 

 denfities of the bodies, eftimated by their fpecific gravity ; 

 and their refraftive power, in refpeft of their denfities, are 

 fet down in fcparate columns. 



Newton's Optics, edit. 3. p. 247. 



M. Euler the younger, purfuing a fcheme fuggeftcd by 

 his father for afcertaining the refratftive powers of tranf- 

 parent liquors, made ufe of two Mcnifcus glades, which 

 he put together when they were plunged in the fluid, the 

 refrafkive power of which he wanted to determine : the 



edges of thefe glaffes being ground flat, they immcdiitsly 

 cohered, fo that none of the fluid could efcape ; and then 

 they might both together be wiped, and ufcd as one objedt- 

 glafs in a long tube, which he could lengthen or (horten at 

 pleafure ; and applying an eye-glafs to it, the whole ob- 

 fervation he had to make was to meafure the exa6t length 

 of his tube, when he could fee through it moft diftinftly a 

 turret, whicli was at a confiderable diftance from him. 

 Or, when the focal diftance was lefs than a foot, he only 

 obfcrved, at what diftance from a wall the image of an op- 

 pofite window was the moft diftintft. Ac. Berlin. 1762, 



P-^302- 



The refratftive power of the fluids which he examined in 

 this manner, he exprefled in the following tables. 



A ray of light palling from air into 



Diftilled water ... 



Rain-water - . . . 



Well-water - 



French wine - - . . 



French brandy ... 



Ditto a ftronger kind - - - 



Reftified fpirit of wine 



Ditto more highly re&ificd 



The white of an egg 



Diftilled vinegar - - . 



A folution of gum arable 



A folution of two fcruples of white fugarl 



in an ounce of water - - j 



A folution of two fcruples of rock-falt, ) 



in ditto - - J 



A folution of tv.'o fci'uples of fait of ) 



urine, in ditto - - ^ 



Oil of Provence ... 

 Oil of turpentine - - - 



The fine of the an- 

 gle of incidence 

 will be to that of 

 refraflion as 



I-33581 



1-3358 



1.3366 



1-3453 

 1.3603 

 1.3646 

 1.3685 

 1.3706 

 1.3685 

 1.3442 

 »-34<57 



o 



J-3457 

 1-3477 



1.3400 



1.4651 

 1.4822 



N. B. The rock-falt and the fait of urine were purified 

 by a double cryllallization. 



The fine of the an- 

 gle of incidence 

 will be to that of 

 refratftion as 



1-33581 



1-3358 



1-3362 



1-3458 



1.3600 



1.3618 



1.3683 



1-3705 

 1-3376 



1.3600 



By a fecond pair of Menifcufes. 



Diftilled water - . . 



Rain-water - - - 



Well-water . . - 



French wine - - - 



French brandy 



Ditto a ftronger kind - - - 



Spirit of wine reftified 



Ditto more highly reftified 



Tea .... 



Mineral alkali faturated ( I fuppofe with | 



water) ... J 



Spirit of nitre ... 



A folution of two fcruples of Glauber's \ 



fait in an ounce of water - \ 



A folution of two fcruples of digeftivel 



fait of Sylvius in ditto - J 



A folution of two fcruples of fal am- 1 



moniac in ditto ' " 3 



A folution of two fcruples of copperas 7 



in ditto - - - J 



Oil of tartar per deliquium 

 Oil of Provence , - - . 



Oil of turpentine ... 

 4E 2 



4-1 

 1.4025 f> g 



'•343° "" 



'•3454 



1.3488 



«'3395 



1-3917 

 1.4648 

 1.4822J 



The 



