184. ENQUIRY INTO THE STRENGTH AND 
beams is as the breadth multiplied by the square 
of the depth; the length being given: and that 
the ultimate deflection is inversely as the depth. 
The power of resisting impact in each iron is 
reckoned by the product of the breaking weight 
multiplied by the ultimate deflection: depending 
upon the supposition that the elasticity remains 
unimpaired; and that the blow, in all cases, 
where the results are to be compared together, 
is given with the same striking body or hammer 
upon beams all of which are equal in weight. 
These suppositions, however, are not strictly 
true, but as the beams are all very nearly of 
equal weight, the product above mentioned will 
give a comparative measure near enough for 
practical purposes; as may be inferred from the 
paper on impact upon beams—Fifth Report of 
the British Association for the Advancement of 
Science.—The modulus of elasticity is given in 
pounds for a base of a square inch; this weight 
may be taken as the measure of the stiffness of 
the iron. It was usually calculated from the 
deflection caused by 112lbs. on the 4ft. 6in. 
bars. 
