JSrom an Increase of Temperature. 371 
specific gravities, the stones were first dried on a sand-bath, and, 
after being weighed in a dry state, they were put into distilled 
water ; and although the pieces of the black and white marble 
weighed about 200 grains, and were left three weeks in water, 
they only absorbed one-tenth of a grain, yet the white marble, in 
particular, gave off a considerable quantity of moisture when first 
heated. The Arbroath pavement absorbed #; of its bulk of 
water, and the Caithness pavement 74; part; which shews the 
great superiority of the latter pavement for all purposes, where 
it is wished to exclude dampness. 
In conclusion, it may be observed that, from the results of the 
experiments given in the Table, it is perfectly evident that not 
the slightest danger can arise from the use of cast-iron in build- 
ings, on account of the difference of their expansion for all ordi- 
nary temperatures. Nor do I think that there is any cause to 
dread the effects of fire where such pillars are used, although that 
was one of the arguments employed to retard their introduction ; 
on the contrary, there is every reason to believe, that even in 
cases where the fire would rage with all the fury that a strong 
wind could impart to it, cast-iron pillars would support the lintels 
of the windows as safely as those of stone, And I do not state 
this as a mere matter of speculation. The late great burning of 
part of the North Bridge New Buildings, is a proof of the cor- 
rectness of the opinion. Of the extraordinary fierceness of this 
conflagration, those who did not witness it might easily have 
satisfied themselves, by inspecting the injury done to the stones 
of the ashler front. I was present at this terrific scene of de- 
struction, before the flames burst from the windows, and remain- 
ed till the fire was quite under the power of the engines. Very 
soon after the flames came sweeping out at the front windows, 
the stones began to crack and skirt off, and a constant shower of 
such large masses fell, during probably half-an-hour, that the 
firemen were obliged to draw back their leathern hose to a con- 
VOL, XIII. PART II. 3B 
