Volume Eleven - Pre-Victorian to the Present Day - some more aspects - Large Testing Machines in South Wales, 1829-1906 . . .

As the poise-weight rolls, the concealed half a ton is gradually released, so that the centre of gravity of the whole steelyard system travels at half the rate of the visible scale. The effect of this is that the scale-unit is double the size that it would be, were a one-ton poise weight acting on the long end of the lever only, and at the same time the required poise is only half the weight.

A further good effect of using a double-arm steelyard in connection with a rolling poise is that the unrecorded inertia resistances are only half of what they would be if a single-armed steelyard were employed with a one-ton weight with its zero on the axis of the steelyard ; for in this case the positive arm of the steelyard would require to be balanced by a stationary counter-weight at the negative end, and the weight of the whole oscillating mass would be approximately double what it is when the poise itself counterweights the lever, by making its zero at the balancing point on the negative end of the steelyard.

The double weight would arise as follows : Firstly, the concealed half-ton of overweight at the long end would need to be balanced by an extra weight of equal amount at the negative end ; secondly, the poise would be doubled in weight ; and, thirdly, the whole lever would require to be made heavier to hold up at its long end a rolling poise of one ton weight with the same stiffness that it holds up the rolling poise of half-ton weights.

To revert for a moment to the comparison between the Cyfarthfa machine of 1829 and the Cardiff machine of 1906.

The similarities in the elemental principles have already been described ; the essential improvements of the latter machine over the former consist chiefly in the introduction of a poise rolling on a double-armed steelyard, and of a movable straining head locked in a sliding frame, by which the clip boxes may be brought close enough to test a rivet, or to any distance apart required for breaking the links of chain cables ; and, of course, also such perfecting the close attention of many workers in this field, amongst whom the author feels particularly indebted to Mr. Thomas Traill, E.E., late Engineer Surveyor-in-Chief to the Board of Trade, and to his successor, Mr. Peter Samson.