Chap. 14.] Prince Rupert's Drop, &c. tf 



metals to this ufe will be mentioned when treating of 

 theni. 



There are two toys made of unannealed glafs/which, 

 though commonly ufed for the amufement of children, 

 exhibit phenomena which juftly intereft the curiofity 

 of the phiiofopher. When a drop of melted glafs is 

 fuffered to fall into water, it aflumes an oval form, 

 with a tail or neck refembling the retort of a chemift. 

 This is called Prince Rupert's drop, and porTefTes the 

 fingular property, that if the fmalleft portion is broken 

 off, the whole drop flies into powder with a kind of 

 explofion, and a confiderable mock is communicated 

 to the hand that grafps it *. The other is called the 

 philofophical phial, which is a fmall cylindrical veflel 

 of glafs, open at the upper end, and rounded at the 

 bottom. It is generally made of glafs fo thick that it 

 will bear a fmart blow againft a hard body without 

 breaking, but if a fmall pebble or piece of flint is let 

 fall into it, it immediately cracks and flies in pieces. 

 This veffel is formed upon fimilar principles with 

 Prince Rupert's drop, it confifts of glafs fuddenly 

 cooled, and, I fufpect, by immerfion in water. 



Various explanations have been offered of thefe 

 facls. The moft generally received is founded on 

 the affumption that the dimenfions of bodies which 

 are fuddenly cooled remain larger than if the cooling 

 had been more gradual. The dimenfions, therefore, 

 of the fmooth external furface of thefe glafies, which 

 are fuddenly cooled, are fuppofed to be larger than 

 is adapted to the accurate envelopementofthe internal 



* Honour is like that glafly bubble, 

 That gives philofophers fuch trouble ; 

 The one part crack'd, the whole will fly, 

 And wits are crack'd to find out why. 



VOL, II. H part, 



