. Transactions of the Institution of Mining Engineers . nute. The unreliability of an inadequately-tested instrument has beenreferred to recently in an important paper read before the Institution,^in which the following statement is made :— Owing to the gross inaccuracy of anemometer readings at low speeds, thefigures for the speeds of air at Pendleton cannot be relied upon within 100 percent, * Third Report of the Committee on The Control of Atmospheric Con-ditions in Hot and Deep Mines : Observations of Temperature and Moisturein Deep Coal-mines/ Trans. Inst. M. E., 1920-1921, vol. I
. Transactions of the Institution of Mining Engineers . nute. The unreliability of an inadequately-tested instrument has beenreferred to recently in an important paper read before the Institution,^in which the following statement is made :— Owing to the gross inaccuracy of anemometer readings at low speeds, thefigures for the speeds of air at Pendleton cannot be relied upon within 100 percent, * Third Report of the Committee on The Control of Atmospheric Con-ditions in Hot and Deep Mines : Observations of Temperature and Moisturein Deep Coal-mines/ Trans. Inst. M. E., 1920-1921, vol. Ixi., page 101. t Ibid., page 112. 1021-1922.] COOPER—THE TESTING OP ANEMOMETERS. 91 In this paper, I shall not deal with the accuracy of air-measurementstaken by the Pitot tube, as the matter has been exhaustively treated in apaper by Dr. A. Rateau.^ The Anemometer Table.—The table may be regarded as adevelopment of that described almost sixty years ago by J. J. Atkinson Z5 TEETH. PITCH 0-628 FOR fkHOUNDLEATHfft B£LT^^^ SECTION OFEPICYCLIC GEAR. PLAN OF FOOTSTEP Fig. 1.—Section of Epicyclic Gear and Plan of , One-quarter Actual Size. and J. It has been designed by Dr. Henry Briggs, and isillustrated by the accompanying drawings and photographs (Figs. 1to 9). Experimental Investigations upon the Theory of the Pitot Tube and theWoltmann Mill, by A. Rateau, Trans. Inst. M. E., 1898-1899, vol. xvii., page124. tThe Velocities of Currents of Air in Mines, Trans. N. E. Inst., 1861-1862,vol. X., page 207. 92 TRANSACTIONS INSTITUTION OF MINING ENGINEERS. [Vol. LXII. The whirling rod on which the meter under test is mounted isrotated by means of a leather sewing-machine belt, I inch in diameter,from a special driving gear (Figs. 1 and 2). Owing to the very widerange required, it was decided to adopt a mechanical rather than anelectrical arrangement for obtaining different speeds. The variable-speed gear, which is worked from a shunt-wound motorthrough a w
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