Page:Micrographia - or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon.djvu/35

Rh that the Box, when the Pipe and that was joyned to it, would contain the Water when fill'd half full, and would likewise without running over, indure to be inclin’d to an Angle equal to that of the greatest refraction of Water, and no more, without running over. The Ruler E F was fixt very fast to the Pipe V, so that the Pipe V directed the length of the Ruler E F, and the Box and Ruler were mov’d on the Pin T T, so as to make any desirable Angle with the Ruler A B. The bottom of this Pipe V was stop'd with a small piece of exactly plain Glass; which was plac’d exactly perpendicular to the Line of direction, or Axis of the Ruler E F. The Pins also T T were drill'd with small holes through the Axis, through those holes was stretcht and fastned a small Wire. There was likewise a small Pipe of Tin loosly put on upon the end of V, and reaching down to the sight G; the use of which was only to keep any false Rayes of light from passing through the bottom of V, and only admitting such to pass as pierced through the sight G: All things being placed together in the manner describ'd in the Figure; that is, the Ruler A B being fixt perpendicular, I fill'd the Box C C with Water, or any other Liquor, whole refraction I intended to try, till the wire passing through the middle of it were just covered: then I moved and fixt the Ruler F E at any assignable Angle, and placed the ﬂame of a Candle just against the sight G; and looking through the sight I, I moved the Ruler R S to and fro, till I perceived the light passing through G to be covered, as 'twere, or divided by the dark Wire passing through P P: then turning the Screw in K, I fixt it in that posture: And through the hole S, I observed what degree and part of it was cut by the cross threads in S. And this gave me the Angle of Inclination; A P S answering to the Angle of Refraction B P E: for the surface of the Liquor in the Box will be alwayes horizontal, and consequently A B will be a perpendicular to it; the Angle therefore A P S will measure, or be the Angle of Inclination in the Liquor; next E P B must be the Angle of Refraction, for the Ray that passes through the sight G, passes also perpendicularly through the Glass Diaphragme at F, and consequently also perpendicularly through the lower surface of the Liquor contiguous to the Glass, and therefore suffers no refraction till it meet with the horizontal surface of the Liquor in C C, which is determined by the two Angles.

By means of this Instrument I can with little trouble, and a very small quantity of any Liquor, examine, most accurately, the refraction of it, not only for one inclination, but for all; and thereby am inabled to make very accurate Tables; several of which I have also experimentally made, and ﬁnd, that Oyl of Turpentine has a much greater Refraction then Spirit of Wine, though it be lighter; and that Spirit of Wine has a greater Refraction then Water, though it be lighter also; but that salt Water also has a greater Refraction then fresh, though it be heavier: but Allum water has a Iess refraction then common Water'', though heavier also. So that it seems, as to the refraction made in a Liquor, the'' Rh