on Steam-Beats, 17} 
guard against accident, when applied to a boiler four feet in 
diameter and twenty feet in length, because the limit given by 
such a column has always been far within the limit of absolute 
safety. The length of the external limb of the mercurial gauge 
has in all cases been proportioned to the strength of the boiler 
and the force to be applied, taking care that the expansive force 
of the steam would displace the mercury long before any dan- 
gerous expansive force would arise. In order to guard against 
the boiler’s-being injured by the action of the fire, from a de- 
ficient quantity of water in the boiler, I have inserted a leaden 
rivet in such a situation that it would melt as soon as it was un- 
covered by the water, and produce an opening which would suf- 
fer the escape of the steam. Although I have made use of boilers 
of this construction, I consider cast-iron boilers safe, provided 
their yarious parts are made of small diameters in proportion to 
their capacity; such for instance as those constructed by Mr, 
Woolf. 
From your knowledge of the subject, do you think you can 
take upon yourself to say, that a high pressure engine with a 
boiler constructed on the principles you have just now detailed, 
would be completely safe for the use of passage -boats? — I 
think equally safe with those called condensing engines, because 
a greater attention to strength is always paid in the construction 
of high pressure boilers than in the construction of low pressure 
boilers, in proportion to the pressure they have to sustain. 
Have not very great improvements been recently made in high 
pressure engines, by which the general mining and manufac- 
turing interests of the country have been greatly benefited ?—I 
think very important ones; the high pressure engine, as con- 
structed by Mr. Woolf, employs not only the expansive force of 
the steam, but also that power which is acquired by its conden- 
sation; and the effect in Cornwall has been, that engines on this 
construction have done double the quantity of work with the 
same quantity of fuel, 
Does your own experience lead you to conclude, that the high 
pressure engine in general js less expensive in point of consump- 
tion of fuel ?—If well constructed they are decidedly ceeconomical 
engines with regard to the consumption of fuel, 
You mean then by this, that the advantage of the high pres 
sure in point of ceconomy in fuel is not confined to engines of 
any one particular construction?—Certainly; I mean it is not 
so confined, 
Have you any connexion whatever with Mr. Woolf ?—None 
whateyer ; I am not personally known to him. 
Have you any reason to suppose that the high pressure steam+ 
engines are already arrived at the degree of perfection of much 
é they 
