C sl jp ) 
would be impoffible for the Stones to fae cold 5 from 
whence it would follow, that being all hot when they 
fell into theSesi, they muft neceflarily fink 5 for it is cer- 
tain that the Heat cannot come into the cavities of the 
fmall Pipes without driving the Air out of them, now 
there being no Common Air in thofe F^ipes while tiie 
Stones are glowing hot, and the faid Stones falling in> 
mediately into the Sea, the Heat is expeU'd by the Water, 
which infiouatesitfelf prefently into thofe Cavities, and 
confequently the Pumice- ftone having its Pipes filled there, 
with, will fink down to the bottom, and- not rife to the 
Superficies of the Water, 
That this is fo, we may be entirely fatisfy'd if we take 
a piece of Wood-coal, that haf been damp'd or extin- 
guiflied, and throw it into the Water, we fhall fee hov/ 
high it will rife, by reafon ot its lightnefs, above the Sti- 
perficies ttiereof. 
This piece of extinguilhed Coal being thrown into the 
Fire till it becomes red hot, all its Tubes or Pipes inftead 
of Air are filled with a fubtile Matter, which I ftiall call 
Fire^ now if you throw that immediately into Water 
the Fire will be expelled from the Pipe$, and fince ther^ 
can be no Vacuum, the Water will immediately fucceci 
therein, and then that fame piece of Wood-coal moft ne- 
ceflarily fink to the bottom. 
Now, that you may the better conceive the cooffgnra- 
tion of the fo called Drj//, or Pumice^ftone, I have placed 
feveral verv fmall Particles thereof before a MicrofcsO. e, 
which it they had been bigger, it would have been i\n- 
pofiible to obferve their (hape. 
Tab. I. Fig. i. A. B. C. D. E. F.G. H. reprefentsa f:ii^]l 
Particle of the fore-mendoned Scone, in which you m <vv 
perceive the very fmall Tubcs^tho by reafon of cheir cxccJ .- 
ing fmallnefs thofe Cavities can be feldom feen, fonje ot 
ihelargeft of them are defcribed between C. and H. and 
the 
