152 Mr Stevenson's Account of the, Explosion of a 
though it must be recollected that this metal, when heated, 
loses much of its strength. On the whole, however, it is pro- 
bable that the entire impulse given by the explosive force, 
could not in this case have been less than 3380 tons on the 
area of the boiler, or about 2 15 pounds upon each square inch 
of its surface. 
The working power of steam in the condensing engines upon 
Watt and Bolton's principle, is now usually adjusted to a pres- 
sure of from S to 5 pounds upon the square inch. But in 
T re ve thick's or Woolf's high pressure engines, where there is 
no condensing apparatus, it is not unusual to work with up- 
wards of 80 pounds on the square inch. The greatest precau- 
tion, therefore, in the application of this principle, becomes ne- 
cessary in the management of the apparatus. 
On the other hand, it may be proper to observe, that acci- 
dents like this of Lochrin, are by no means beyond the power 
of remedy. If proper attention were paid to the safety-valves, 
and to the obvious and simple indications of the mercurial gauge, 
and if the firemen were regular in supplying the boiler with fuel 
and water, the risk of explosion might with considerable certainty 
be avoided. 
Notwithstanding the numerous improvements upon the steam- 
engine which are daily making, it is still a desideratum in the 
use of the steam-boiler to construct a safety-valve, which shall 
depend as little as possible upon the engine-men for the certain- 
ty of its operation. For this purpose, Mr Adie suggests, that 
a piece of plate-copper might be introduced into the manhole of 
the boiler, the strength of which should be previously so adjusted 
that it shall give way when the expansive force of the steam ex- 
ceeds about one-half tnore than the pressure at which it is in- 
tended to be wrought. For the greater safety of those near the 
boiler, a wooden or metallic pipe might be connected with this 
plate or regulator, which should be made to rise 12 or 14 feet 
above the boiler. Although this description of safety-valve 
would, perhaps, when occasionally thrown off, deprive us for a 
time of the use of the boiler ; yet the object of the greater safety 
of persons in its neighbourhood would be attained. 
Si me the preceding part of this article was read before the 
