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IX. On the existence of an element of Strength in Beams subjected to Transverse 
Strain, arising from the Lateral Action of the fibres or particles on each other, and 
named by the author the ‘Resistance of Flexure' By William Henry Barlow, 
Esq., F.R.S. 
Received February 23, — Read March 29, 1855. 
It has been long known, that under the existing theory of beams, which recognizes 
only two elements of strength, namely, the resistances to direct compression and 
extension, the strength of a bar of cast iron subjected to transverse strain cannot be 
reconciled with the results obtained from experiments on direct tension, if the neutral 
axis is in the centre of the bar. 
The experiments made both on the transverse and on the direct tensile strength of 
this material have been so numerous and so carefully conducted, as to admit of no 
doubt of their accuracy; and it results from them, either that the neutral axis must 
be at, or above, the top of the beam, or there must be some other cause for the 
strength exhibited by the beam when subjected to transverse strain. 
In entering upon this question, it became necessary to establish clearly the position 
of the neutral axis, and the following experiments were commenced with that object; 
but they have led to others, which are also described herein, and which establish the 
existence of a third, and a very important element of strength in beams. 
I was desirous that the experiments for determining the position of the neutral 
axis should be made on such a scale and in such a manner as to place this question 
beyond doubt ; and with this object the following means were adopted : — 
Two beams were cast, 7 feet long, 6 inches deep, and 2 inches in thickness ; on 
each of which were cast small vertical ribs at intervals of 12 inches : these ribs were 
one-fourth of an inch wide, and projected one-fourth of an inch from the beam. In 
each rib nine small holes were drilled to the depth of the surface of the beam, for the 
purpose of inserting pins attached to a delicate measuring instrument; the intention 
being to ascertain the position of the neutral axis by measuring the distance of the 
holes in the vertical ribs when the beam was placed under different strains. The 
measuring instrument consisted of a bar of box-wood, in which was firmly inserted, 
at one end, a piece of brass, carrying a steel pin ; and at the other end a similar piece 
of brass carrying the socket of an adjusting screw. The adjusting screw moved a 
brass slide, in the manner shown in Plate XII. which carried another pin similar 
to that inserted in the box-wood bar, at the other end of the instrument. The 
instrument was first made entirely of brass; but the effects of expansion from the heat 
of the hand were so sensible, that the wooden bar was substituted. The pins on the 
instrument fitted loosely into holes in the beam ; and the mode of using the instru- 
