Page:Philosophical Transactions - Volume 010.djvu/88

(334) times 'tis made of a piece of wire, that a little beneath the bottom of the Ball is bent round, so as to stand horizontally, that, the Guiny being laid on it, it may be supported by it, as the foot is by a stirrup; and in this way a piece of Coin is the most readily put on and taken off. But the more secure way is, instead of the bent wire, to imploy a very short piece of Brass with a broad slit in it, capable of receiving the edge of the Guiny, which wish one turn or two of a small and slight lateral screw may be kept fall in it, and readily, the operation being ended, taken out again.

If you desire to examine not only Guinys, but greater Gold-Coins and Metalline mixtures, it would be convenient, that the undermost stem and the screw be made by it felt, that it may be at pleasure thrust upon the stem and taken off again. For by this means, if the ball of the Instrument be made large enough, you may have room to put on, as occasion shall require, one, two or three flat and round pieces of Copper, Lead, &c. with each of them a hole in the middle, fitted to the size of the stem, so that they may be put on as near the lower part of the ball, as you think fit, and then the screw may be thrust on after them, not only to take hold of the Coin or Metalline mixture to be examined, but to support the plate, if need be; and by a variety of such plates, which may be taken off and put on at pleasure, the same Instrument, if (as I was saying) the ball be competently large, may be adjusted sometimes to a Guiny, sometimes to a Coin of Gold or Silver, or to a Metalline mixture twice or thrice as heavy as a Guiny in the Air.

The Instrument being made of a convenient bigness and shape; to adjust it for the use of examining Guinys, you must by the help of the stirrup or screw, hang, at the bottom of it, a piece of that Coin which you know to be genuine, and, having carefully stopt the Orifice of the stem, if it be a pipe, (that no water may get in at it,) immerse the Instrument leasurely and perpendicularly into a Vessel ful of clean water, till it be deprest almost to the top of the stem, and then letting it alone, if being setled it continue in the same station and posture, your work is done, but if it sink quite under water, you must lighten it either with a file,