Mr Fairbairn on Fireproof Warehouses. i 
not less than 3-10ths, effected in the quantity of material 
used. 
Having pointed out the strongest form of beams as applied 
to fireproof buildings, it will be necessary in this place to 
refer to their strength, and to inquire into the nature of the 
strains to which they are subject. It has already been 
stated, that iron beams in warehouses have two distinct 
forces to contend against, that of direct pressure and the 
force of impact; with the former there is no difficulty, but 
the latter involves a proposition on which mathematicians 
are not agreed. For practical purposes we may, however, 
suppose a case, such as a large cask of molasses, or box of 
heavy mineral substance, equal to one ton = 2240 lbs,, fall- 
ing from a height of six feet upon the floor. Now, according 
to the laws of gravity, a body falling from a state of rest 
acquires an increase of velocity, in a second of time, equal 
to 32 feet, and during that period falls through a space of 
16 feet: this accelerated velocity is as the square roots of 
the distances, and a falling body having acquired a velocity 
of 8 feet in the first foot of its descent, and 6 feet being the 
height from which a weight of one ton is supposed to fall, 
We have J 6 = 2.449 x 8 = 19.592 for the velocity in a 
descent of 6 feet. 
Then, 19.592 x 2240 = 43,886 lbs., or nearly 20 tons, as 
the momentum with which the body impinges on the floor. 
In the present state of our knowledge, this momentum can- 
not probably be taken as the measure of the force of impact, 
but we may fairly estimate the latter as exceeding that of 
momentum ; and having these forces to resist, it will be ne- 
cessary to guard against them, and to make the beams, 
columns, and arches in the lower floors, of such strength as 
will resist the blow, and neutralize its effect upon the floor. 
Although the iron beams and arches of a fireproof floor 
may be sufficiently elastic to resist an impinging force, such 
as above described, it is still advisable to adopt other pre- 
cautions, such as the bedding of timber along the top of the 
 arches,* or to form the two lower floors entirely of wooden 
* Since the above was written, I have been informed that the Act of 
