on Steam- Boats. x i73 
eonstructed, with sufficient safety-valves adapted to it, the ope- 
ration of which the man could not impede, would it have been 
liable to accident ?—I feel some difficulty in answering such a 
question as that, because I am afraid that there are so many 
technical terms in engine-making, and reasons why safety-valves 
should be attended to, that I doubt whether they would net go 
to more evil by the man not having access to them than by theit 
being open to him. 
If there was one safety-valve which was not accessible to the 
engineer, and another which was, would not that danger be pre- 
vented ?—I would beg to explain, by saying, that on board the 
Regent, which has a large boiler, I found it necessary to have 
two safety-valves, and sometimes I put three safety-valves: to 
make it quite easy for the man to move the valve, I have a sort 
of bell-pull going down to the place where he stokes, to pull it 
up every hour if he pleases, to keep it in action, because it is 
clear the spindle may corrode and stick fast fot want of use. 
Supposing it not touched once a week, it is not a safety-valve 
any longer, because a very little friction will add a great matiy 
pounds weight to the opposition the steam ought to meet with. 
According to your experience and knowledge, would a low 
pressure engine be safe in most cases that can occur ?—I never 
knew a low pressure engine unsafe, but it appears that high 
pressure engines have been. : 
Would a high pressure engine, under the same circumstances, 
be equally safe ?—Certainly not. 
Do you conceive there is any difficulty in constructing a safety- 
valve in such a manner as that the engineer shall be able to keep 
it in constant fitness for its action, without having a power to 
fasten it down and prevent it from acting ?—I conceive that the 
same motive which would induce the engineer to work it with an 
improper pressure, would induce him to leave it untouched, that 
it might have an improper pressure. I beg to state, that there 
is not that difference between a high pressure and a low pressure 
engine, as to its power, that is generally supposed; because it is 
understood, that the steam in the boiler is kept at from four to 
six pounds upon the inch, but from two and a half to four is 
quite abundant for any use a low pressure engine can be wanted 
for: then, if an engine is in any thing like working order, there 
is a vacuum formed by the engine itself, by the construction, 
that causes an addition of ten pounds the inch. On the lowest 
calculation, those two added together, make fourteen pounds ; 
if you take high pressure steam at forty pounds the inch, you do 
not, in my opinion, get additional force in proportion to the risk 
incurred ; because we well know, that if the boiler be of cast 
iron, faults will unavoidably arise in casting which you ¢gannot 
: see, 
