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alfo hold(though the difparicy be not fo great and coSfpicuous) 
in reference to other Metals,as Lead and Tinn, that differ in fpe- 
cifick Gravity. 
To give at once an Inftance of the Truth and life of this No- 
tion, I was induced to fit the Inftrument, that was grounded on 
it,for the examination of Guinys, which are by far the moft ufu- 
al Gold-Coins that pafs in 'EngUnA^ And though the exaftnefs 
and diligence of our Ingenious Friend Mn Slingsby allows us to 
expeft, that no injury that care and skill can prevent fliall be 
done to that Coin, yet becaufefomeColdrnuths and others re- 
tain fears of being deceived by the fraudulent and Tub tile Artifi- 
ces of falfe Coiners,! thought it might not beariiifs to furnifli 
them with aneafie and praftical way of diftinguifliing a true 
Guiny from a counterfeit. And though I hope I need not tell 
you, that I look not upon the Inftrument I fliew'd you at Gre- 
JhAm Colledge^ as capable of examining Gold and other Metals 
with as much nicety as by other Methods one may Hydroftati- 
cally do; yet this little Trifle may on fome occafions be prefer- 
able, fince the Inftrument, which is not dear, being once fitted, 
there is no need to have either exaft Scales, or skill inHydro- 
ftacicks, or any knowledge of Arithmetick, and yet the diffe- 
rence of a true Guiny from a counterfeit will not only be fuf- 
ficient!y,but confpicuoufly,made to appear, and the operation 
will be ijjuch fooner performed than in the other way, and very 
much fooner and cheaper than by the Methods commonly employ- 
ed by Goldfmiths and Refiners* For,in our way the Coin is 
notdefac'd or injur'd by cutting, pnnching, &c 5 nor is there 
any need of Touchftones, or Aqua fortis, and yet the tryal is fo 
quickly made, that perhaps near twenty Guinys may be examin- 
ed one by one, in about a quarter of an hour : I fay, one hy cne^ 
becaufe thatif thelnftrumerltbedefignedand fitted for fuch a 
purpofe, Guinys may be tried 4^ (?;;r^, But whether the 
Goldfmiths will make ufeof this way, I leave them to determine ; 
it being fufficient for me, to have gratified fuch Virtuofi, efpeci- 
ally the Difciples of Vulcan, as have given occafion to expcft 
this Trifle will be acceptable unto them ; and to add this In- 
ftance to thofe I haveelfewhere given by way of proof, That by 
Xx 2 the 
