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VIII. Account of Experiments on Torsion and Flexure for the Determination of Rigidities . 
By Joseph D. Everett, D.C.L., Assistant to the Professor of Mathematics in the 
University of Glasgow. Communicated by Sir William Thomson, F.B.S. 
Received January 25, — Read February 7, 1867. 
In my Paper read February 22nd, 1866, the intention was expressed of continuing my 
experiments on rigidity with a modified form of apparatus. This intention was carried 
out during the past summer, and I have now to report the results. 
In the former experiments, the rod operated on was supported at both ends, and was 
bent or twisted by hanging a pair of equal weights so as to act symmetrically on both 
ends ; and the amounts of flexure and torsion were measured by the movements of two 
images formed by reflection upon a screen. 
In the new apparatus, the rod was firmly held at one end in such a manner that this 
end could undergo no movement whatever, while the other end was acted on by a 
couple composed of the direct action of a weight and the upward pull of one arm of a 
balance produced by weighting the other arm. The effect produced was observed, as in 
Kirchhoff’s experiments, by means of two telescopes looking down into two mirrors 
which reflected a scale of lines crossing each other at right angles placed horizontally 
overhead. 
A B (Plate IX. fig. 1) is the rod operated on, entering a socket in the cylindrical iron bar 
C, in which it is firmly secured by screws (three in each set) which clamp it at two places 
about 2 inches asunder. The other end A passes through a brass socket (shown in cross 
section at fig. 2), to which it is also secured by screws in two places. This socket forms 
part of a piece of brass, which is shown on a larger scale in longitudinal section in fig. 3, 
where n is a point or cone to be supported by a ring (M, fig. 1) hanging from one arm of 
a balance, while the lower part consists of a short cylinder m (for receiving the crosspiece 
shown in fig. 4 and indicated by dotted lines in fig. 3) terminated by a screw which 
receives the nut pp. The circular hollow shown in the centre of the cross piece (fig. 4) 
fits the cylinder m, and the crosspiece can either be rotated about it or slipped off on 
loosening or removing the nut. The four arms of the crosspiece are all of equal length, 
and each of them has on the upper side near the end a cone or point for supporting a 
weight by means of a ring. F F is a cast-iron box, on the top of which the cylinder C 
rests in two notches one at each end, in which it turns freely when not secured by the 
clamp G. H is a graduated circle for turning the cylinder (and with it the rod A B) 
through any required angle. K, L are two mirrors clamped to the rod, and adjustable 
by footscrews into any position nearly parallel with the rod. One of them is shown on 
