94 
Temperature of three cold nails 3°. Of the other three 40°. 
Fall of hammer 10 inches. 
Result. Two cold nails broke. Three warm nails broke. 
Series 12. Experiment with fresh nails. Twelve cooled 
for four hours to 3°. Twelve others 41°. Fall 7 inches. 
Result. Seven cold nails broke. Eight warm nails broke. 
The collective result is that 21 cold nails broke and 20 
warm ones. 
The experiments of Lavoisier and Laplace, of Smeaton, 
of Dulong and Petit, and of Trough ton, conspire in giving a 
less expansion by heat to steel than iron, especially if the 
former is in an untempered state. Such specimens of steel 
wire and of watchspring as I possess expand less than iron. 
But this, as Sir W. Fairbairn observed to me, would in certain 
limits have the effect of strengthening rather than of weak- 
ening an iron wheel with a tire of steel. 
The general conclusion is this — Frost does not make 
either iron (cast or wrought) or steel brittle, and that acci- 
dents arise from the neglect of the companies to submit 
wheels, axles, and all other parts of their rolling stock to a 
practical and sufficient test before using them. 
“On the Effect of Cold on the Strength of Iron,” by 
Peter Spence, F.C.S., &c. 
In the conversation at the last meeting of the Society 
on one of the causes of railway accidents, namely, the 
breaking of the tires of the carriage wheels, there was a 
general expression of opinion that the reduction of tempera- 
ture during frost had the effect of reducing the strength of 
iron, and that this was the proximate cause of these 
occurrences. Dr. Joule, on the other side, stated that 
however general the impression might be, he knew of no 
experiments that tended to prove that impression to be a 
correct one. 
It seemed to me that a few experiments on cast iron 
