14 
little more than 301bs. per square inch, from which it will 
be seen that great strength in a boiler is not now so requisite 
as formerly, and particularly when it is considered that the 
same accidents will happen to the strongest as well as to 
the weakest boilers, from similar causes, and that when 
they happen to a strong one, the explosion is the more 
terrific in the direct proportion as the boiler is the stronger. 
We should therefore avoid the cause of these dreadful 
accidents rather than strengthen the boilers. Now, there 
is one very great disadvantage in the cylindrical boilers, viz., 
that the incrustation will all collect in that portion of the 
boiler whch is nearest the fire, and being a non-conductor of 
heat, will expose that portion of the boiler which lies 
between the fire and such incrustation to be burnt away. 
The argument in favour of this boiler, derived from " the 
ease with which it may be repaired," is therefore more than 
done away with by its so often standing in need of that 
repair which in well constructed boilers will not be 
required for the first 12 or 14 years. The next and last 
boiler I shall at present occupy your time in considering, is 
that of the Cornish boiler. It consists of an outer cylin- 
drical case, having an inner tube passing through its whole 
length, in one end of which the fire bars or gxate is placed, 
by which arrangement the heated air and flame is made to 
pass nearest the surface of the water in the boiler, where 
both air and water are the hottest ; the former then returns 
through the side flues, and, descending under the grate, 
passes under the boiler last, where both the heated air and 
water are at their coolest, so that in a boiler of suflicient 
length the whole heat given out by the fuel may, under this 
arrangement of the flues, be imparted to the water in the 
boiler, and it is consequently found in Cornwall that they 
may be used to advantage to the extent of Jifti/ feet in length. 
I am induced to appear before you on this subject in conse- 
quence of my not having found these points hinted at 
either in the very excellent practical work on steam-engine 
boilers by Mr. Armstrong of Manchester, or elsewhere. I 
may here also mention the very great importance it is 
to the ovmers of steam-engines that the iron selected for 
these boilers should be of a proper quality for that purpose, 
for I have known many instances of the bottom of boilers 
being entirely worn out in 18 months, instead of lasting nearly 
as many years, the kind of boilers in both instances 
being in every respect the same, from which circum- 
stance there can be no doubt that it is on the real 
stamina of the iron from which the boilers are made 
that their goodness or goodfornothingness depends. Con- 
nected with this subject is that of the chimney, which 
is very often carried to the height of 160 and 200 feet, and 
consequently made so small in the internal flue at the top 
