340 SEVENTH REPORT—1837. 
give from 7 to 9 tons per inch, results not widely differing 
from those above ; they are noticed with some suspicion by Mr. 
Tredgold (Essay on Strength of Cast Iron, pages 91 and 92), 
who concludes from reasoning on the transverse strength of 
cast iron, according to the theory which he had adopted, that 
the direct tensile strength must be 20 tons or more. Mr. 
Barlow too, whose reasoning has better foundation than Tred- 
gold’s, concludes, whilst he gives these gentlemen’s results, 
that the strength must be upwards of 10 tons per square inch, 
(Treatise on the Strength of Timber and other Materials, art. 
128), Iam not aware of any objection which can be brought 
against the tensile results given above, except some slight 
error which Mr. Barlow conceived (in his earlier work on the 
Strength of Timber, &c.) might arise from the use of testing 
machines, and that, in this case, would affect but four of the ex- 
periments; all the rest were made upon Mr. Fairbairn’s lever. 
I hope to explain the cause of this difference of opinion among 
our ablest inquirers at a future meeting. 
The resistance of materials to a crushing strain is equally 
a matter of doubt. Rondelet found (Traité de l Art de batir) 
that cubes of malleable iron, and prisms of various kinds of 
stone, were crushed with forces which were directly as the 
area, whilst from Mr. Rennie’s experiments, both upon cast 
iron and wood, it would appear that the resistance increases, 
particularly in the latter, in a much higher ratio than the 
area, (Mr. Barlow’s Treatise, Art. 112). 1 have endeavoured, 
by repeating with considerable variations the ingenious ex- 
periments of Mr. Rennie, to arrive at some definite conclu- 
sions. 
In order to effect this, it was thought best to crush the 
object between two flat surfaces, taking care that’ these were 
kept perfectly parallel, and that the ends of the prism to be 
crushed were turned parallel and at right angles to their axis, 
so that when the specimen was placed between the crushing 
surfaces its ends might be completely bedded upon them. 
For this purpose a hole 13 inch diameter was drilled through 
a block of cast iron about 5 or 6 inches square, and two steel 
bolts were made which just filled this hole, but passed easily 
through it; the shortest of these bolts was about 1} inch long, 
and the other about 5 inches; the ends of these bolts were © 
hardened, having previously been turned quite flat and per- 
pendicular to their axis, except one end of the larger bolt 
which was rounded. The specimen was crushed between the 
flat ends of these bolts, which were kept parallel by the block 
