( 334 ) 
times 'tis ii^ade of a piece of wire, that a little beneath the bot- 
tom of the Ball is bent round, fo as to ftand horizontally, that, 
the Guiny being laid on it, ic may be fupported by ir, as the 
footis byaftirrup; and in this way a piece of Coin is theraoft 
readily put on and taken off* But the more fecurc way is , in- 
ftead of the bent wire, to imploy a very ihort piece of Brafs 
with a broad flit in it, capable of receiving the edge of the Gu i - 
ny, which wiih one turn or two of a fmall and flight lateral 
fcrew may be kept faft in ir,and readily,the operation being end- 
edjtaken out again. 
If you defire to examine not only Guinys, but greater Cold- 
Coins and Metalline mixtures, it would be convenient, that the 
undermofl fl:em and the fcrew be made by it felf,that it may be at 
pleafure thrufl upon the ftem and taken ofFagain. For by this 
means, if the ball of the Inftrument be made large enough, you 
may have room to puton,as occafion ftall 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 fize of theflrero, fo that 
they may be put on as near the lower part of the ball,as you think 
fir,and then the fcrew may be thrufl: on after them,not only to take 
hold of the Coin or Metalline mixture to be examined , but to 
fupport the plate, if need be ; and by a variety of fuch plates, 
which may be taken off and put on at pleafure , the fame Inftiru- 
ment, if (as I was faying) the ball be competently large,may be 
adjuftcd fometimes to a Guiny, fometimes to a Coin of Gold or 
Silver, or to a Metalline mixture twice or thrice as heavy as a 
Guiny in the Air. 
The Infi-rument being made of a convenient bignefs and fliape; 
to adjuft it for the ufe of examining Guinys , you muft by the 
help of the ftirrup or fcrew, hang, at the bottom of it, a piece of 
that Coin which you know to be genuine^and, having carefully 
ftopt theOrificeof the ftem, if it be a pipe,(tl3at no water may 
get in at it,) immerfethe Inftrument leafurelyand perpendicu- 
larly into a Veflel ful of clean water, till it be depreft almoft to 
the top of the fl:em, and then letting it alone, if being fetled it 
continue in the fame ftation and pofture, your work is donejbuc 
if it fink quite under water, you muft lighten it either with a file, 
' or 
