The PREFACE. 
that the Box, »when the Pipe and that was joyned toit, would contain the 
~ Water.when fill’d half full, and would likewife, without running oyer, in- 
dureto be inclin’d to an Angle , equa) to that of the greateft refraction of 
Water, and no more, without running over. The RulerE F wasfixt very faft 
to the Pipe V,, fo that the: Pipe V. direGed the length of the RulerE.F;and 
the Box and Ruler were movd on the Pin TT, fo as to make any defi- 
rable,Angle-with the Ruler AB. The bottom of this Pipe V was ftop'd 
- with afmall piece of exa@ly plain Glafs , which was plac'd exactly per- 
pendicular to the Line of direction, or Axis of the Ruler E F.:, The Pins 
alfo TT. were drill’d with {mall holes through the 4.x7zs,and through thofe 
holes wasftretcht and faftned afmall Wire. There was likewife.a {mall 
Pipe of Tin loofly put onupon the end of V, and. reaching downto the 
fight G 5, the ufe ef, which was only. to’ keep any falle,Rayes of light from 
pafling through the bottom of V, and only.admitting {uch to pals.as, pier- 
ced through the fight G: All things being placed together in. the manner 
defcrib'd in the Figure 5, that is, the Ruler AB being fixt perpendicular, I 
fill’d the Box CC with Water, orany other Liquor, whofe refraction Iin- 
tended to.try, tillthe Wire pafling through the middle of it were: juft co- 
vered.;! then moved and fixt the Ruler F E at any affignable Angle;. and 
placed the flame.of,.a Candle juft againft the fight.G 5 and looking through 
thefightd,: I:moved the-Ruler.R $.to and fro, till I perceived the light paf-, 
_ fing through.G tobe:covered, as ‘twere, on divided. by the dark Wire: paf-, 
fing through |P.-P: then turning the Screw in K, I. fixt it in that pofture: 
And.through the hole S$; Lobferved what degree and part of it was cut by, , 
the crols threads in.S.,,And: this gave,.me the Angle of Inclination, APS 
an{wering to the Angle of Refraction; BP E):. for the, furface of the Liquor. — 
in the.Box will be alwayes horizontal , and ‘confequently AB will bea 
perpendicular to its. the Angle.therefore APS will meafure,, or be the 
Angle of Inclination inthe Liquor; next E PB. muftbe the Angle of Re- 
fraction,for the Ray that pafles throughthe fight G, pafles alfo, perpendicu- 
larly through the Glafs Diaplragme. at. F., and confequently alfo perpendi- 
cularly through the lowez furface of the Liquor contiguous to the Glafs, and 
therefore fuffersno refraction till'it meet with the horizontal furface of the 
Liguor in'C.C, whichis determined-by the two Angles. ee i 
By means of this Inflrument I can with\ittle trouble, ‘and avery 
Small quantity of any Liquor, examine, moft accurately, the refrattion 
of it, not only for one inclination, but for all; and thereby am inabled 
to make very accurate Tables; feveral of which Ihave alfo experimentally 
made,and find, that Oy! of Turpentine has amuch greater Refrattion 
then Spirit of Wine’; though it be lighter’; and that Spirit of Wine 
has a greater Refraction then Water, though it be lighter allo 3 but that 
falt Water:al/o has agreater Refrattion then treth, thoughitbe heavier's 
- but Allum water bas a le refrattion then common Water, though bea 
vier alfowSo that it. feems,as to the refraction madein a Liquor,the {peci-\ 
| f: : fick 
