95 
could without much difficulty be made, and which might 
set the matter at rest one way or the other. 
I therefore decided on having some lengths of cast iron 
made of a uniform thickness of |in. square, from the same 
metal and the same mould; these I obtained after a good 
deal of trouble, on account of the moulders being off work 
at new year’s time, and this must be my excuse for not 
being able to give due notice of my communication. 
Two of the four castings I got seemed to be good ones, 
and I got the surface taken off, and made them as regular 
a thickness as was practicable. 
I then fixed two knife-edged wedges upon the surface of 
a plank, at exactly nine inches distance from each other, 
with an opening in the plank in the intervening space, the 
bar being laid across the wedges a knife-edged hook was 
hung in the middle of the suspended piece of the bar, to 
the hook was hung a large scale on which to place weights. 
The bar was tried first at a temperature of 60 Fahr. ; to 
find the breaking weight I placed 561b. weights one 
after another on the scale, and when the ninth was put on 
the bar snapped. This was the only unsatisfactory experi- 
ment, as 14 or 281bs. might have done it, but I include it 
among the others. I now adopted another precaution, by 
placing the one end of the plank on a fixed point and the 
other end on to a screw-jack, by raising which I could, 
without any vibration, bring the weight to bear upon the 
bar. By this means, small weights, up to 71bs., could be put 
on while hanging, but when these had to be taken off and a 
large weight put on, the scale was lowered to the rest, and 
again raised after the change was made. I may here state 
that a curious circumstance occurred twice, which seems to 
indicate that mere raising of the weight, without the slightest 
apparent vibration, was equal in effect to an additional weight. 
3fcwts. were on the scale, a 141b. weight was added, then 
71b., then 41b., 21b., lib., and lib., making 4cwts. and lib. 
This was allowed to act for from one to two minutes, and 
then lowered to take off the small weights, and replaced by 
