290 / Securities against Fire, fyc. 



7. In what follows in this article I speak with diffidence. I have 

 merely hinted in my letter, that iron beams have been employed in 

 houses, to prevent the progress of fires. I now add, what I recollect 

 to have heard, that a building in England furnished with iron beams 

 and having in it a number of stories, being inflames, the floors fell 

 in together; and again, we have been told lately, of a conservatory 

 for plants near London, surmounted by a dome framed with iron, 

 which suddenly fell in, no fire having concern in the event. — This 

 has led me to suspect the operation of a new principle, in these ca- 

 ses, to which, perhaps, due attention has not yet been paid ; name- 

 ly, the expansibility of iron in consequence of an increase of its tem- 

 perature ; notwithstanding iron is the least susceptible of expansion 

 of any of the common metals. In the case of the inflamed building 

 having different stories, (as mentioned above) ; even it it were ascer- 

 tained that its iron beams were placed, some horizontally and some 

 perpendicularly, still it will be allowed to be possible that all of these 

 beams were not heated alike, as being placed at different distances 

 from the main body of the fire ; and in this case, a want of symmetry 

 in the expansion of the different beams may have led to a contra- 

 riety of action in different parts of some of the main supports of 

 the building, in consequence of which the downfall in question oc- 

 curred. 



In confirmation of this hypothesis I relate what follows. 1. The 

 celebrated Thomas Paine once had in his possession an iron bar of 

 more than one hundred feet in length, which he placed in a horizon- 

 tal position on rests, along the side of a brick wall ; and fastening one 

 end of it immoveably in the wall, he left the other end free to move 

 itself; when he found the free end so much affected by the changes 

 of temperature in the air, that it served him as a sort of thermometer 

 as to the temperature of the atmosphere. 2. An engineer in the ser- 

 vice of the United States has lately proved by observation, that when 

 a coping-stone of great length is used for covering the upper tier of 

 masonry in a wall, it cannot at times be prevented from shrinking, 

 so as to leave a chasm between itself and the next coping-stone, by 

 which rain can have access to the walls.* 3. The frequent differ- 

 ence of opinion of men of science and artists as to the cause of the ex- 



* It should be observed here, that it has been said, that some stones are capable of 

 imbibing a great quantity of water, with little alteration in their dimensions. 



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