MR. AIRY’S ACCOUNT OF THE HARTON EXPERIMENT 
;i52 
ceived that the two “ Means of the two lines” are almost strictly independent of tem- 
perature. Now we have, in the Harton Experiment, other means of determining the 
relation between the pendulums. In article 45, 
Log. 
Rate Pendulum 8 below ^ ro 
Rate Pendulum 1821 
Log. 
Rate Pendulum 1821 below 
Rate Pendulum 8 above 
= 0-00073694. 
Subtracting the first from the second, and dividing by 2, the effect of the mine is 
eliminated, and that of temperature is sensibly eliminated ; and we obtain 
Log. 
Rate Pendulum 1821 
Rate Pendulum 8 
0-00072568. 
This agrees so nearly with the result of Comparison A, as greatly to increase the pre- 
sumption that some change took place in one pendulum after the Seventh Series. 
75. Let then be the increase (in units of the 8th 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=«x 75'19, 
whence z=7‘37 nearly 
=^ of the correction employed in our tables. 
As the mean excess of temperature at the lower station in the Harton Experiment 
was 7°' 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 
whence ^=2-7236. 
And the Earth’s mean density (article 62) will result 6-809. 
76. If, however, we used Comparison B in the same way, we should have 
133=^X83-75, 
whence 2=1-59 nearly, 
or the alteration to be made in the Earth’s mean density is less than one-fourth of 
that resulting from Comparison A. This gives for the Earth’s mean density 6*623 
nearly. 
