502 ON THE EXPLOSION OF THE BOILER 
excessive pressure, arising probably, from the 
accumulated force of the steam having no outlet 
through the safety valves. And, he calculates, 
that, if the boiler was sound, the pressure of the 
steam could not be less than 387 pounds, on the 
square inch; and that it would require a pressure 
of at least 939 pounds, on the square inch, to pro- 
ject the engine, by one single impulse of the steam, 
to the height of 30 feet ; the area of the aperture, in 
the roof of the fire-box being 1619 square inches, 
and the weight of the engine being 153 tons. 
3. The body of the boiler was a cylinder, 8 feet 
53 inches in length, and 3 feet 6 inches in diame- 
ter; and, supposing, that, at the time of the ex- 
plosion, there was very little water on the top of 
the fire-box, and neglecting the thickness of the 
steam pipe, which passes through the steam in the 
boiler, then the height of the segment of the boiler 
filled with steam, would be about 1 foot 4 inches ; 
and, therefore, in this part of the boiler, there 
were nearly 26 cubic feet of steam. The top of 
the fire-box was 3 feet 5 inches, by 3 feet 3 inches ; 
and this was the base of the cupola of the boiler, 
the sides of which were 2 feet high, and the top 
of which was groined in a parabolic curve, the axis 
of which was 2 feet in height; and, therefore, in 
