[ i8 4 ] 
Pores of the Drop, and prevents the fudden Com- 
munication of the exterior Fluids with the imprifoned 
igneous Matter j and as Glafs cannot be ground with 
very fine Emery and Oil, but by long rubbing ; fuch 
rubbing heats the Drop, and gradually opens the 
Pores fo as to grant an infenfible Paflage to the igneous 
Matter, whereby the Drop becomes at laft in the fame 
Cafe with nealed Glafs j and in the Cafe in which 
itfelf is, when it is put into the Oven to be nealed. 
When a Glafs-Drop is made, by fufpending it in 
the Air only, it does not break fooner than nealed 
Glafs : Becaufe as this fmall Mafs of Glafs retains its 
Heat a long while in the Air, the Heat ferves as a 
Nealing-Oven, and keeps its Pores dilated long 
enough for the igneous Particles to find a free Paflage. 
The Principles, by which I have accounted for the 
Effects of the Glafs-Drop, are not confined to this 
Phenomenon alone : They are more general than 
is commonly imagined. Some Corollaries, which I 
(hall deduce from them, will prove what I advance. 
Steel, like the Glafs-Drop, acquires its Hardnefs by 
being plunged into Water : And if Melf. Mariotte and 
Homberg had compared them together in this Cir- 
cumftance alone, they had been in the right. 
The mod celebrated natural Philofophers, in order 
to account for the tempering of Steel, have had re- 
courfe to different Arrangements of its Parts produced 
by the Fire, and fixed, by the Co ] d of the Water, in 
the new State, in which the violent Heat had put 
them. 
J 
The 
1 he 
3 
