from 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 g-V of its bulk of 

 water, and the Caithness pavement -^\ Y 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. 3 b 



