2.36 
MR. W. H. BARLOW ON THE RESISTANCE OF FLEXURE 
to obtain a formula for computing, approximately, the breaking weights of these 
girders, without first ascertaining their deflection. 
Using the same letters as before, we have, for the resistance due to tension, 
and for the resistance to flexure. 
|( 
Y j I I ^ \ . 
and consequently, for the united effect of the two resistances, 
I shall therefore conclude these observations by comparing the breaking weights 
computed for tensile resistance alone, and those obtained from the formula which 
includes the resistance to flexure, with the actual breaking weights obtained by the 
experiments, taking the value of /'= 18,750 lbs., and (p = 23,000 lbs. 
Description of beam 
or girder. 
Breaking weight if the 
resistance depended on 
direct tensile strength. 
Breaking weight com- 
puted hy the formula, 
including the resistance 
to flexure. 
Breaking weight I 
as obtained by the | 
experiments. j 
lbs. 
lbs. 
lbs. 
No. 1 
849 
1890 
1888 
No. 2 
1308 
2567 
2468 
No. 3 
1808 
3287 
3084 
No. 4 
2912 
4659 
4353 
No. 5 
2578 
4935 
5141 
No. 6 
3819 
5533 
5147 
No. 7 
4031 
5919 
6000 
The accordance exhibited by the computed and the actual breaking weights, 
evinces the general accuracy of the formula, as applied to this form of beam ; while 
these results, compared with those computed for direct tensile force alone, show how 
large a proportion of the strength of cast iron, when subjected to transverse strain, 
is due to the resistance arising from the lateral action. 
It wilt also be seen that comparisons of the relative strengths of different forms of 
section, calculated, as has been customary, on the assumption that the resistances 
are constant forces, or governed by a constant coefficient, must be entirely fallacious. 
It was my intention to have included in this paper a similar investigation as to 
the position of the neutral axis, and the amount of the resistance arising from lateral 
action of the fibres in wrought iron ; but as the experiments will take some time 
to complete, and as the facts elicited in reference to cast iron are of sufficient import- 
ance to render it desirable that they should be made known, I will reserve the 
examination of wrought iron for the subject of another communication. 
