from an Increase of Temperature. 355 



desired to report to the Dean of Guild on the subject, and the 

 proprietor requested my father to calculate the comparative ex- 

 pansibility of the cast-iron pillars and the stone, for a considera- 

 ble alteration of temperature. Sufficient data were easily got for 

 the rate of expansion of cast-iron ; but the only experiments which 

 could then be found on that of stone, are contained in a short notice 

 by M. Destigny, in the 7th volume of the Quarterly Journal of' 

 Science, Literature, and Art. These are not extensive, and have, 

 moreover, been determined by taking the difference between the 

 expansion of the stones and rods of iron and copper to which 

 they were attached, thereby diminishing quantities naturally very 

 small; and the difference was again augmented and rendered 

 more visible by a double system of levers ; a method liable to 

 many objections in point of accuracy, even though the experi- 

 ments were performed with great care. 



Since the date of the interdict formerly referred to, the almost 

 universal adoption of cast-iron supports in constructing elegant 

 fronts for shops, and the perfect manner in which they have been 

 found to answer the purpose, has given that practical refutation 

 to the alleged objections which, in such cases, is always most to 

 be relied on. And although I do not recollect that, in any in- 

 stance, a fire has taken place in a building, the front of which was 

 supported on cast-iron, yet, from the experiments I have made, 

 it will be seen that, even under such circumstances, the iron is 

 not likely to be hurtful from the excess of its expansion over 

 that of stone. Nevertheless it appears to have been a common 

 opinion till within a very recent period, and one which has been 

 supported by names of the very highest authority, that the length 

 of a rod of Carrara marble could not be sensibly altered in length 

 by a change of temperature. This opinion was founded on a 

 very beautiful speculation on the arrangement of the crystals of 

 marble ; and although none of my experiments tend to show 

 that it is correct with regard to either of the specimens of Car- 

 rara marble which I have examined, yet the supposition may not 



VOL. XIII. PART II, z z 



