Account of pendulum experiments undertaken in the Harton Colliery, for the purpose of determining the mean density of the earth, by G. B. Airy
Sect II. Comparisons of the Upper and Lower Clocks. <s>27</s>25. In the ordinary state, the galvanic circuit was interrupted at both circuit-breakers. At the pre- arranged minute for commencing signals, as nearly as possible, each of the observers completed the connexion, and then gave his attention to the galvanometer. The movement of the needle, at intervals of 15s nearly, assured each observer that the other was prepared to observe: and every observation of the clock-time of the movement of the needle was then efficient for comparison of the two clocks. Only, it was necessary to know precisely, when the time of examining the written record of the time-signals should arrive, <u>which</u> were the <u>corresponding</u> observations of the same galvanic current. For this purpose, the following instructions were given. After observing the clock-times of a few signals, the upper observer interrupted the circuit during one signal only, and then restored the connexion. The lower observer, after waiting one or two minutes, did the same thing. After another short delay, the upper observer interrupted the circuit during two signals. The lower observer, after a short delay, did the same.
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Account of pendulum experiments undertaken in the Harton Colliery, for the purpose of determining the mean density of the earth, by G. B. Airy, 1855. From The Royal Society, PT/54/5
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