from an Increase of Temperature. 367 



From the results given in the Table, it is evident that no 

 danger is to be apprehended from a change of temperature af- 

 fecting cast iron and sandstone, in a very different degree, as 

 their expansion, in so far as regards all building operations at 

 least, may be considered as the same. The difference between 

 the expansion of bricks and malleable iron amounts only to 

 .00042 for 90° F., or half an inch on 100 feet ; and Roman 

 cement, when in as damp a state as all buildings must be, will 

 expand more than malleable iron, since it did so in my experi- 

 ment, even after it had been dried for eleven hours at a tempe- 

 rature of 207°. This, therefore, will in a great measure serve for 

 an explanation of the fact mentioned by Mr Brunel, in describ- 

 ing his method of constructing arches, by suspending the courses 

 of brick with straps of hoop-iron, viz. that he had had some anxiety 

 as to the manner in which variations of temperature would affect 

 his mode of operating, by expanding the metal more than the 

 brick and mortar ; but, on examining his experimental arch, both 

 in summer and in winter, not a crack was to be seen. The sub- 

 stances at the bottom of the Table are black marble, and the rod 

 of Wedgewood's ware ; their expansions are nearly alike, and 

 they expand very nearly half as much as platinum for the same 

 number of degrees.* 



M. Destigny mentions in his paper before alluded to, that 

 he found the expansion of stone not at all affected by a difference 

 in its state of humidity. From what I have observed in con- 

 ducting my experiments, I am quite of a different opinion, for 

 although no increased expansibility was observed by wetting 

 sandstone after it had been dried, and I did not try any direct 

 experiment of this nature with any of the marbles, on account of 

 the very small quantity of water which they were found to ab- 



* I have since procured another rod of Galway black marble, which contained 

 more fossils, and was softer than the first. Its expansion for 180° F. was .0004793. 

 and for 1° F. .00000266. 



