Philosophical Transactions of the Royal Society of London

    I am now enabled to fulfill the intention expressed (vol. cli. p. 678) in concluding the above ‘Account,’ as read to the Royal Society, having since then completed a series of experiments upon the compression of specimens of the Holyhead Rocks, and determined their moduli of elasticity. These experiments were made upon cubes cut from solid and perfect pieces of the rocks by the lapidary’s wheel, each 0·707 inch upon the edge—each side, therefore, presenting a surface of 0·5 square inch,—and the utmost care being taken to preserve perfect parallelism between the opposite boundary planes, so that, when compressed between hardened steel surfaces, fracture should not result by inequality of pressure. The compressions were made at the Royal Arsenal, Woolwich, with the very accurate and excellent machine used for testing compression and extension of metals in the gun-factory; and I have to express my thanks to Lieut.-Col. Anderson, C. E., the Superintendent of that department, for the valuable assistance afforded me through his attention.

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