VI, A Caution to be ufed in examining the Spe - 
cifick Gravity of Solids , by weighing them in 
Water . By James Jurm, M. D . R. & Seer. 
A S it is oftentimes of good Ufe to know the Spe- 
cifick Gravity of folid Bodies, a great Num- 
ber of Experiments have been made upon this Subjedt 
by Members of the Royal Society , and other Curious 
Perfons ,* the Refult of which has been publifh’d in fe- 
veral Tables in th e PhilofophicalTranfa&ions, and elfe* 
where. But, as it is neceflary that Experiments of 
this Nature fhould be made with great Exadfcnels, if 
we would fo far depend upon them, as to draw any 
Inferences from them in Natural Philofophy, it may 
not be amifs to mention a Caution, which is often- 
times neceflary in the making of them, and which I 
have Reafon to think has been generally very little re- 
garded. It is this ; That when a dry, porous Body 
is to be weigh’d in Water, in order to difcover its Spe- 
cifick Gravity, it is nece/Iary, by fome means or other, 
to extricate the Air out of all the fmall Pores and Ca- 
vities within it, that the Water may have free Liberty 
to enter and pervade them. Unlefs this Care be ta- 
ken, it muft needs happen, that the Air, which pof- 
fefles thofe fmall Cavities, and keeps the Water out, 
will render the Solid of lefs Weight in the Water, and 
confequently of lefs apparent Specifick Gravity than 
it really is. The bed way of avoiding this Inconveni- 
ence, is, to fet the Veflel of Water, in which the fo- 
