C 363 j 



what is mod remarkable is, that when the pieces of 

 glafs are thick, and ftrong enough to refill: the (hock, 

 they are marked by the explofion, with the moft 

 lively and beautiful colours, generally covering the 

 fpace of about an inch in length, and half an inch 

 in breadth. 



In fome of the pieces which he was fo obliging 

 as to fend me, thefe colours lie all intermixed and 

 confufed ; but in others I obferve them to be dif- 

 pofed in prifmatic order, in lines parallel to the courfe 

 of the explofion, and in fome (as N° 1.) I have 

 counted three or four diflin<£t returns of the fame 

 •colour. 



He has lately informed me, that, fince he fent 

 me this piece, he has (truck thefe prifmatic colours 

 into another mafs of glafs, in a ftill more vivid and 

 beautiful manner, the colours (hooting into one an- 

 other. This efFecl:, he fays, was produced by making 

 a fecond explofion, without moving any of the ap- 

 paratus after the firft. 



When the glafs in which thefe colours are fixed 

 is examined, it is evident that the furface is mattered 

 into thin plates, and that thefe give the colours, the 

 thicknefs of them varying regularly, as they recede 

 from the path of the explofion. 



In the middle of thefe coloured fpots (as in N° 2.) 

 fome of thefe thin plates, or fcales, are (Truck off, I 

 fuppofe by the force of the explofion j and with the 

 edge of a knife they are all eafily fcraped away, 

 wtren the furface of the glafs is left without its poliili 

 (asinN°3.) 



The piece of glafs on which I have marked thefe 



numbers, as well as that on which he has firuck the 



A a a 2 colours 



