150 
Mr Stevenson's Account of the Explosion of a 
partments of about 4 inches in breadth, were left without 
perforations. These holes being, at the same time, pier- 
ced only about one inch and a quarter apart ; almost as much 
of the iron at the seams or joinings was, by this means, cut 
into rivet-holes as was left in an entire state. We may 
add, that if this boiler, which was made with materials of great 
strength, had been more judiciously put together ; if fewer 
rivets had been employed, and if ‘the bars across the bottom, 
marked letter a in the section, Fig. 1. Plate 17. had been ri vet- 
ted and otherwise strongly connected with the horns or points 
of the crescent bottom, it might have resisted a much greater 
strain than it was calculated to sustain. 
In building or constructing steam-boilers, the work should be so 
laid out by the artist, that the plates may break joint, if we may 
apply a technical term in masonry to this operation ; or, in other 
words, the plates of which the boiler is to be formed should be 
so arranged, that the end-joint of one plate may fall into the 
middle of the two adjoining plates. If attention were paid to 
this arrangement, the plates of the top and bottom would 
form part of the sides, and the vessel would possess much addi- 
tional strength, at the expence, perhaps, of but a little more 
labour. In preserving the strength of the plates, great attention 
should also be paid to the punching or perforation of the holes 
in good order, that the seams may fit each other. The punch 
or chisel for this purpose, should be uniformly cylindrical, or 
have as little taper towards the point as possible ; so that the 
fibre or texture of the iron may not be deranged in perforating 
the rivet-holes. When iron is unduly stretched in this operation, 
it produces an effect similar to what workmen term cold-short ; 
and has a direct tendency to lessen the strength of the portions 
of iron remaining between the holes. These holes ought also, 
invariably, to be pierced, so as to run in a zig-zag or alternate di- 
rection, instead of being ranged in straight lines, as is sometimes 
done. 
< To show still farther the utility of these observations, let us 
suppose that a horizontal section of the boiler at Lochrin con- 
tained 324 square inches of iron. After making every allow- 
ance for rivet-holes of the diameter of Jths of an inch, perforated 
at the distance of about 1 inch and 1 th apart, we find, from the 
