Experiments for determining the Length of the Pendulum. 415 
This may serve as a specimen of the method, and I shall only 
extract the final results of the observations of a few days. 
1817. August 20th. 54°58’ 30” 
30th. 54 58.3 
Sept. Ist. 54 58 35 
2d. 54 58 28 
Sth. 54 58 27 
24th. 54 58 26 (see above.) 
Oct. 6th. 54 58 28 
Oth. 54 58 32 
Méan 54 58 29 
This exactly agrees with the mean of the results of 16 single 
meridian altitudes taken with the same instrument, and with the 
results of several hundreds of observations made with an excel- 
lent sextant of Ramsden’s which belongs to the Institution. 
I am, sir, ; 
With due respect, your obedient servant, 
EpwarD RIDDLE, 
Oct. 21, 1818. Master of the Trinity-House School, 
Newcastle-upon-Tyne. 
LXIV. An Account of Experiments for determining the Length 
of the Pendulum vibrating Seconds in the Latitude of London. 
By Capt. Henry Kater, F.R.S. 
{Concluded from p. 370.} 
Havine thus satisfied myself that no injury to the knife-edges 
was to be apprehended from moderate use, the pendulum was 
_ again suspended, but now, to my surprise, I found the number 
of vibrations different from what they were before the remeasure- 
ment. This difference became still greater on the following day ; 
and it at length occurred to me that the moisture of the atmo- 
sphere must have undergone some change, and that an alteration 
had been thus occasioned in the weight of the wooden extremi- 
ties of the pendulum. On referring to the register of the hygro- 
meter kept by Mr. Browne, it was found that a considerable 
change had in fact suddenly taken place from moisture to dry- 
ness; and so great was the derangement of the pendulum from 
this apparently trivial cause, that it became necessary to move 
the second weight. This was accordingly done, and the follow- 
ing experiments made for again bringing the number of vibrations 
to an equality. 
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