APPENDIX. 353 
ji. And fince as was above obfcrved in 
Experiment III. Number 15. the Air with 
the Preffure of one Acmofphcrc, ruflics into 
a Vacuum^ at the Race of 1505 Feet in a 
Second of Time, with the Impulfe of thefe 
1857 Acmofpheres, it would in 'vacuo have 
a Velocity of four hundred and fifty four 
Miles in a Second. And how much greater 
mufl: the Velocity of expanding Gun Powder ^ 
be, which moves with fo irrefiftible an Im- 
petus. 
In order to eftimate how much the 
Shell of the Bomb mighr contrail by the 
Coldnefs of this freezing Mixture, I layed an 
Iron Back of a Fire Stove, which was of 
caft Iron, on a Mixture of pounded Ice and 
Salt, and covered it with the fame, the Cold 
made it contrad Ith of an Inch, i. e. ^th 
part of its Length, which was twenty five 
Inches. Whence by Calculation I found, 
the Capacity of the contrafted Shell was 
0.265 cubic Inch lefs, viz. j^th part left, 
than that of the fame unconcraded Shell. 
And the Shell of Ice within fide, at, the 
fame time dilating about j^th of its Bulk, the 
Bomb mufi: necelfarily burlt. 
A a 53. In 
