88 
of the tire on the wheel of the break-van of the Great 
Northern Railway. 
In our attempt to investigate the cause of the failure it 
may be interesting to show how the experiments on 
wrought iron to which we have referred were obtained at 
various temperatures, and subsequently to give the results 
as found in the summary. 
The immense number of purposes to which both iron and 
steel are applied, and the changes of temperature to which 
they are exposed, renders the enquiry not only interesting 
in a scientific point of view, but absolutely necessary to a 
knowledge of their security under the various influences of 
those changes, and when it is known that most of our metal 
constructions are exposed to a range of temperatures vary- 
ing from the extreme cold of winter to the intense heat of 
summer, it is assuredly desirable to ascertain the effects 
produced by those causes on material from which we 
derive so many benefits, and on the security of which the 
safety of the public frequently depends. It was for these 
reasons that the experiments in question were undertaken, 
and the summary of results are sufficiently conclusive to 
show that changes of temperature are not always the cause 
of failure, as that which occurred near Hatfield on the Great 
Northern Railway. 
That such is the fact, I may adduce several accidents of 
broken tires all of which occurred during the spring and 
summer months when the temperature was high. One of 
them occurred on the Lancashire and Yorkshire Railway in 
the summer of last year when the temperature was 50° to 60° 
above freezing. I could enumerate others in which the 
winter frosts had nothing to do with the fractures which 
ensued. 
It might have been satisfactory to have shown the process 
by which the following results were obtained, suffice it to 
observe, that all the specimens were torn asunder with and 
