173 
Steam Engine, 
Steam engines on Mr. Trevethick’s plan require a 
boiler of immense strength ; for they work with a power 
sometimes equal to 60 pounds on the square inch, while 
common engines, even Mr. Watt’s, seldom work with 
more than 5 pounds. We are happy to state, however,, 
that the present accident arose, not from the impossibility 
of making a boiler strong enough, but from a culpable 
mismanagement of a boy appointed to attend the engine. 
Impatient to finish his work, he had put a piece of timber 
between the top of the safety valve and a beam above it, so 
that it could not rise to allow steam to escape tvhen pro- 
duced in greater quantity than required. He even went 
away to fish in the river. In the mean time the engine 
was stopped by another workman, who knew not what 
the boy had done, and in a short time the mischief we have 
stated followed. The boy had returned, and was in the 
very act of removing the piece of wood he had so impru- 
dently put over the valve when the explosion took place. 
He was the least hurt of all who were near the spot. 
This accident ought to serve as a warning to engineers, 
to construct their safety valves in such a manner that com- 
mon workmen cannot stop them at their pleasure ; which 
may be easily done. 
From the way in which part of the boiler was bent, 
which was constructed of cast iron nearly an inch in thick* 
ness, it is thought the steam must have acquired an ex- 
pansive force equal to 500 pounds on the square inch be 
fore it gave way- — a force much beyond any that caii be 
required. But though this shows that engines on Mr. 
Trevethick’s plan, may, with proper precautions, be 
worked with as much safety as those on the common 
principle, such an accident as the one we have stated can- 
not fail to intimidate some people from adopting them. It 
is therefore with much pleasure we state that a boiler on 
a new construction, calculated to bear a much higher de^ 
