(6o 5 )

made very flcndcr, that the different Depresfions of the Instrument in theWater may be the more Notable. And for the sime reason, it ought not tobe too Shcirt, efpeciaily if it be to be applied to other Ules than the Examin-ing of Guinys.

1 At the Undermost of the two IIolcs in the Ball, is Inserted and Soder’d theundermost part of the Instrument, which I call the Serem, or the Stirrup .The Serem F, is a very short piece of Braß with a broad Siit in it, capablc•f receiving the edge of the Guiny, which with one turn or two cf a final land stight lateral Screw may be kept fast in it, and readily the Operation be-ing ended, taken out agam. The Stirrup G is made of a piece of Wirc,that a little beneath the bottom of the Ball , is bent round, (ö as to standHorizontally, that the Guiny may be laid on it.

It would be convenient, that the undermost Stem and the Serem be made byit (elf, that it may be at pleafitrc thatst upon the Stem and taken off again.For, by this means, it the Ball of the Instrument be made large cnough, youmay have room to put on for Ballast, as occasion fliall require, one, two, orthree flat and round pieccs of Copper, Lead, iste, with each of them a holein the middle sitted to the Size of the Stem, Ib that rhey may be put on asnear the Lower part of the Ball as you think fit, and then the Serem may bethrust on aster them, not only to take hold of the Coin or Metalline mixtureto be Examind, but to support the thin Flates.

To adjust this Instrument for the use of examining Guinys, which are byfar the most usüal Gold Coins that paß in England, you muff by the help ofthe Stirrup or Screm, Hang, at the bottom of ir, a piece of that Coin whichyou know to be Genuine, (and having caresully stopt the Orifice of the Stern<if ic be a Pipe) that no Water may get in at it) Immerse the Instrument lel-iiirely and perpendicularly into a Veffel füll of clean Water, till it beDeprestalmost to the top of the Stern, and then letting ic alone, if, being Setled, itcontinue in the lamc Station and Posture, your vvork is done. If it Emerge,you muff add a little weight to it, either by putting into the Stern, if it beHollow, forne Dust Shot, Filings of Lead, or some other Minute and HeavyBody, or eise by putting on the (hört Stern abovementioned, that comes outbeneath the Ball, a flat, round and perforated piece of Lead, of Weight suf-ficient to enable the Guiny to Depress the weight as Low as its desired : Butif it Sink quite under Water, you must lighten it either with a File, or byseraping or grating off a little of the Ballast Plate abovementioned; or, ifyou have put any Weight into the Cavity to poise it, by taking out lomeof that, till you have made it Light enough : This being done, a Mark HIs to be made just at the place where the Surface of the Water touches theStern, and then taking out your Instrument , substitute in the place of yourGuiny a little round Plate of Brass, of the (äme Weight, or a Grain or twoheavier, in the Air ; and putting the Instrument into the Water, as before,suffer it to Settle, and malte another Mark I. at the Intersection of the Sternand the Horizontal Surface of the Water.

There may (though ’tis like there very seldom will) happen a Gase, where-in, though the Principle, our Instrument is framed on, will hold good, ytc

the:

Ftf. l?5-

fig, 1 96 .

Fif. in-