Account of pendulum experiments undertaken in the Harton Colliery, for the purpose of determining the mean density of the earth, by G. B. Airy
Log Rate Pendulum 1821/Rate Pendulum 8 = 0.00072568. This agrees so nearly with the result of Comparison A as greatly to increase the presumption that some change took place in one pendulum after the Seventh Series. 75. Let then z be the increase ( in units of the 8<sup>th</sup>. decimal of the logarithm) which ought to be made for every degree of temperature. Taking the difference between the two first lines of Comparison A, 554 = z x 75.19 whence z = 7.37 nearly = 1/28 of the correction employed in our tables. As the mean excess of temperature at the lower station in the Harton Experiment was 7<sup>o</sup>.13, the correction to be added to the rate below is 53, or the correction to the gravity is 106. Therefore (see article 45), Log Gravity below/Gravity above = 0.00002358, or Gravity below/Gravity above = 1.00005429 Using this number in the equation of article 60, 0.00006603 = 0.00017984 x d/D whence D/d = 2.7236. And the Earth's mean density (article 62) will result 6.809.
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Manuscript details
 Author
 George Biddell Airy
 Reference
 PT/54/5
 Series
 PT
 Date
 1855
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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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