678 PHILOSOPHICAL TRANSACTIONS. [ANNO 174Q. 



touch each other; they swim, as it were, in a flood of this matter of fire; and 

 for this reason it is, that melted glass affects the colours of flame. 



When this substance is exposed to the air, the coolness of this fluid, which 

 touches the surface of the glass, cools that surface first; that is, brings the par- 

 ticles nearer together, braces their pores, and thus imprisons the particles of fire, 

 which still fill the inside of this substance. While these fiery particles find pores 

 enough on the surface to move freely, the glass continues whole; but when the 

 glass grows colder, that is, when the pores of its surface begin to confine these 

 fiery particles; then their whole action is exerted against the parts of the glass, 

 which they break into a thousand pieces. In order to avoid this bursting, no- 

 thing more is requisite than to keep the pores on the surface of the glass wide 

 enough, that the fiery particles may pass through, and fly off" insensibly. Now 

 this is what is done by putting the hot piece of glass into an oven, the moderate 

 heat of which keeps these pores open to a certain pitch, and yet allows the glass 

 to acquire its due consistence in this state of middling porosity, in which consists 

 the annealing of glass and other fused substances. 



Hence it appears, that all unnealed glass carries within itself its principle of 

 destruction, which is the matter of fire imprisoned. But the glass drop is in 

 this respect, in a worse case still than imnealed glass; for besides that it has not 

 been exposed to this secondary heat, which keeps its pores open, till the glass 

 has acquired its due consistence, for fear that the coolness of the air alone should 

 not close its pores soon enough and imprison a sufficient quantity of the igneous 

 matter, it is suddenly thrown into cold water, which by its coldness and weight 

 is fitter than the air to produce such an effect speedily and effectually. Hence 

 the only surprising circumstances in these glass drops is, that any of them remain 

 without breaking, by the great quantity of igneous matter suddenly shut up in 

 them by the cold water. And indeed this accident befalls more than the half of 

 them; and those that escape doubtless owe their preservation to the spherical or 

 cylindrical figure of the compact shell, which the coldness of the water forms on 

 their surface; for it is well known that this figure produces an equality of resist- 

 ance on all sides, which considerably increases the resisting force; and this is the 

 first reason why, as soon as this equilibrium is broken, either by rubbing away 

 one side of this surface, or by making a hole in it, or, in fine, by breaking the 

 small end of the drop; the resistance is instantly overcome, and the igneous 

 matter, imprisoned within the glass, and constantly on the strain against it, 

 bursts it into powder. 



This destroyed equilibrium is but one disposition that favours the effect of the 

 imprisoned igneous matter; but the communication which is opened for it with 

 ti)e subtile exterior fluids, rouses this matter which is in a state of inactivity, 

 developes its spring, kindles it somewhat in the manner of the phosphorus, which 



