94 Captain Hall’s and Mr Henry Foster’s Experiments 
As the whole pendulum had acquired a coating of oxide, with 
the exception of the tail-piece, which was lackered, I was de- 
sirous of ascertaining in what manner and to what degree its 
vibrations would be effected by this partial addition of weight ; 
and, for this purpose, the following experiments were made. 
The vibrations of the pendulum, in its oxydized state, having 
been determined, 10 grains of weight were affixed at two-thirds 
of the length of the bar (measured through the ball) from the 
point of support, that being supposed to be near the centre of 
oscillation of the oxide. This had for its object to discover, be- 
fore cleaning the pendulum, what would be the effect of an ad- 
dition of weight at that place. On swinging it, accordingly, the 
number of vibrations was increased 0,83 in 24 hours. It was 
then taken to the Mint, and the weight, carefully determined 
by Mr Barton, in one of his delicate balances, was found to be 
15 lb. 10 oz. 14 dwt. grains. It was next cleaned by Cap- 
tain Kater, by means of diluted sulphuric acid, and afterwards 
washed with a solution of soda in water ; and, being effectually 
dried, was again weighed, when it was found to have lost exact- 
ly 24| grains. Coincidences wxre now taken on three succeed- 
ing days, and the number of vibrations of the pendulum, in its 
clean state, proved to be fewer than when it was coated with 
oxide, by only 0,73 of a vibration. Since no more than one- 
fifth part of the oxide removed could be oxygen, only one-fifth 
of the above difference between its vibrations when clean and 
when coated, or 0,14, can be ascribed to additional weight, 
since it was formerly swung in 1820 ; the real difference, how- 
ever, to be accounted for being 0,97, this cause is manifestly in- 
adequate to the effect. I have therefore thought it right, after 
attentively considering every other possible manner in which the 
pendulum could have been altered, to adopt the idea which h'ad 
been suggested, and which was eventually proved to be correct, 
since the knife-edge, upon removal after the experiments were 
over, was found to be distinctly rounded. To obtain the most 
correct results, I have accordingly used the vibrations made in 
London, in 1820, to compare with the experiments made before 
the accident, and the vibrations recently determined in London, 
for comparing with those made after it, — an arrangement ren- 
dering the resulting ellipticities entirely independent of that cir- 
cumstance.” 
