PENDULUM AT THE ROYAL OBSERVATORY, CAPE OF GOOD HOPE. 155 
wood let into the wall. I have little doubt but that the good going of the 
clock was by these means in a great measure secured. On each side of the 
pendulum, somewhat above the middle of it, were suspended two of Jones’s 
thermometers. The disk was formed of a small circle of card paper about 
three-tenths of an inch in diameter, this measure being found to be the best 
and most convenient. Instead of the wooden stand for supporting the small 
telescope, through which the coincidences, or rather the disappearances and 
re-appearances of the pendulum-rod and the disk are noted, as well as the 
magnitude of the arc of vibration, a small thick brick pier was raised so as to 
receive the plate to which the telescope is attached. The usual adjustments of 
the clock, pendulum and telescope, being completed, we were now ready to 
commence. 
I here deem it right to notice the very able assistance which I received from 
Captain Ronald : his exertions were truly praiseworthy ; I cannot recommend 
them too highly. I likewise avail myself of paying a just tribute to the aid 
which was afforded by Lieutenant Johnson, of the Honourable East India 
Company’s Service, now superintendant of the observatory at St. Helena. 
This gentleman being on a visit to me, very kindly at my request took an 
active part in all the observations. 
The sheets accompanying this short paper must be considered as the united 
labours of Captain Ronald, Mr. Johnson, and myself, and the responsibility of 
each as to accuracy must depend upon the papers signed with the observer’s 
name. As far as I am able to judge of these things, the near agreement of 
three independent series of observations is no small argument of their ac- 
curacy. 
It must not for a moment be conceived that I reckon our results as in any 
way final in the determination of the compression of the earth, inasmuch as it 
would be advisable to begin a new series of observations (say) in the midst of 
winter, or what would be better, in different seasons of the year, lest the coeffi- 
cient for temperature might require some correction ; though even this test can 
hardly be supposed, from the experiments made by Captain Sabine on this very 
pendulum in London, to be required. I have ever been of opinion, (how far 
correct or not, I leave others to judge,) that the invariable pendulum ought 
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