COHESION 



dropped into cold water [exhibiting a "Prince Rupert's 

 drop,"( 9 ) (Fie. 13)], and if I take one of these little tear- 

 like pieces and break off ever so little from the point, the 

 whole will at once burst and fall to pieces. I will now 

 break off a piece of this. [The lecturer nipped off a small 

 piece from the end of one of Rupert's drops, whereupon the 



FIG. 13 



FIG. 14 



whole immediately fell to pieces.] There ! you see the solid 

 glass has suddenly become powder, and more than that, it has 

 knocked a hole in the glass vessel in which it was held. I 

 can show the effect better in this bottle of water, and it is 

 very likely the whole bottle will go. [A 6-oz. vial was filled 

 with water, and a Rupert's drop placed in it with the point 

 of the tail just projecting out; upon breaking the tip off, 

 the drop burst, and the shock, being transmitted through 

 the water to the sides of the bottle, shattered the latter 

 to pieces.] 



Here is another form of the same kind of experiment. 

 I have here some more glass which has not been annealed 

 [showing some thick glass vessels ( 10 ) (FiG. 14)], and if I 

 take one of these glass vessels and drop a piece of pounded 

 glass into it (or I will take some of these small pieces of rock 

 crystal; they have the advantage of being harder than 

 glass), and so make the least scratch upon the inside, the 

 whole bottle will break to pieces it can not hold together. 

 [The lecturer here dropped a small fragment of rock 

 crystal into one of these glass vessels, when the bottom im- 



" Pnnce Ruperfs Drops." These are made by pouring drops of melted 

 green glass into cold water. They were not, as is commonly supposed, in- 

 vented by Prince Rupert, but were first brought to England by him in 1660. 

 They excited a great deal of curiosity, and were considered " a kind of 

 miracle in nature." 



10 Thick glass vessels. They are called Proofs or Bologna phials. 



