1819.] of ‘Cast-Iron Shafts ir Machinery. 201 
gentlemen, very justly regarded-as at the head of their profession, 
using as little cast-iron in the construction of their engines as 
possible. But it may be said, “ why so much caution and hesi- 
tation about a matter of this kind? Why was not the question 
put beyond all doubt by actual experiments. We have been in 
the habit of ascertaining the lateral strength of cast-iron by 
means of apparatus constructed for the purpose ; for instance, 
all joists used in fire-proof buildings are proved by lateral preg- 
sure, why not then the beams of steam-engines in the same 
manner !” 
The torsional strength too of such shafts as are used in mill- 
work can be proved by wrenching. These reflections are natural 
enough; and I was aware that experiments had been made to 
ascertain the facts proposed, although I knew little of the 
results; and even if I had, still the necessity of my making 
similar experiments would not have been superseded, for this 
reason, that having occasion for a number of shafts in the 
summer of last year, my object was not to ascertain the strength 
of cast-iron shafts generally, but the strength of these particular 
shafts as nearly as possible, and to have them proved in 
such a manner as to be certain that they were of the strength 
required. 
i had, therefore, an apparatus fitted up for the purpose, which 
merely consisted of two pine logs, with a strong square socket of 
cast-iron fixed to the side of each, about two feet from the end; 
one of them served to hold the shaft, whilst the other, having an 
iron hook fixed to the end of it, 14 feet 2 inches from the 
centre of its socket, acted as a lever to wrench the shafts. 
These logs, supported about four feet from the ground, lay level 
and parallel with each other; and whilst the one end of the 
shaft was held by the one socket, the other end of it rested with 
its collar upon the edge of a plank, and the lever was applied upon 
the square of the shaft, and close to the side of the plank, so as 
to prevent as much as possible any lateral stress. The weight of 
the lever, or rather its effective weight, was ascertained by letting 
its hook rest on the scale of a balance, whilst its other end was 
upporved upon a knife edge in the middle of the socket, and its 
effective weight thus ascertained was 120 lbs. To the hook at 
the end of the lever, in making the experiments, weights were 
suspended, and increased by not more than 2 lbs. at a time. 
Having got this apparatus finished, in order to ascertaim the 
strength of such shafts as are usually cast in Glasgow, two bars 
of cast-iron, about five feet long each, the one 3, and the other 
41 inches square, were turned in a lathe at five different places, 
and each place differed in diameter from the next. to it by a 
quarter of an inch. Upon the cylindrical parts of these shafts, 
the experiments were made, and the following are the parti 
culars. 
