JSrom 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. Desrieny, 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% 
