290 Securities against Fire, &c. 
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 ita number of stories, being in flames, 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 its 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 if 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 Wttle alteration in their dimensions. 
