. Transactions of the Institution of Mining Engineers . 1921-1922.] COOPER THE TESTING OF ANEMOMETERS. 97 Comparison of Different Anemometers.—The following series of testswas carried out in order to obtain charts for different sizes of instru-ments, and 6-inch and 4-inch meters of similar design were used (Fig. 4),while two 2f-inch meters of the usual design were also included. The four anemometers tested were all in regular use—one 2|-inchand the 6-inch at the Heriot-Watt College and the 4-inch and the second2f-inch at collieries. The radius selected at which to place the meters was 5 feet 5
. Transactions of the Institution of Mining Engineers . 1921-1922.] COOPER THE TESTING OF ANEMOMETERS. 97 Comparison of Different Anemometers.—The following series of testswas carried out in order to obtain charts for different sizes of instru-ments, and 6-inch and 4-inch meters of similar design were used (Fig. 4),while two 2f-inch meters of the usual design were also included. The four anemometers tested were all in regular use—one 2|-inchand the 6-inch at the Heriot-Watt College and the 4-inch and the second2f-inch at collieries. The radius selected at which to place the meters was 5 feet 5 inches,giving a circumference of travel of 34 feet, and the speeds recordedranged from 50 to over 2,000 feet per minute. As the first-mentioned velocity is very low for anemometer reading, itwas found during the tests that only instruments in good working orderwould give satisfactory results at that speed. Of the four anemometerstested, only the 4-inch and 6-inch meters yielded consistent figures at. Vc/oc//)^ in Feet pur Minute,. Fig. 8.—Charts of Four Anemometers, this low rate of speed; this was probably due to the former being a newinstrument and to the latter having lately been overhauled. The results given by the two small instruments were unreliable, andrequired unworkably large corrections at low speeds. When a velocity of 500 feet per minute is reached (Fig. 8), thecorrections for all four instruments become fairly uniform, and remainso up to the maximum velocity of over 2,000 feet per minute. An interesting point in connexion with those experiments is that,although the charts plotted from the tests are similar in form to thosesent out by the makers of the instruments, the figures of correctiondiffer widely. This is particularly so at low speeds, and also at therecorded velocities of crossing the line of zero correction. In these experiments the effect of impact of the air due to the massof the rod and meter has been neglected, as it was considered that acorrect
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