364 G. B. Airy on Pendulum experimenis, etc. 
was a small apparatus for breaking circuit. At times fe insebon 
arranged, the circuit was completed by this apparatus at both 
Stations, and then it was the duty of the observers at bath sta- 
tions to note the clock times of the same signals; and these evi- 
ently give comparisons of the clocks, and therefore give the 
means of comparing their rates. ‘Thus (by steps previously ex- 
plained ), the number of swings made by the upper pendulum is 
compared with the number of swings made in the same time by 
the lower pendulum 
Still the result is not complete, because it ech be influenced 
by the peculiarities of each pendulum. In order to overcome 
these, after pendulum A had been used above and pendulum B 
below, they were reversed; pendulnm B being observed above 
and A below ; and this, theoretically completes the operation. 
But in order to insure that the pendulum received no injury in 
the interchange, it is desirable again to repeat the experiments 
with A above and B below, and again with Babove and A below 
In this manner the pendulums were observed with 104 hours 
of incessant observations, simultaneous at both stations, A above 
and B below; then with 104 hours, B above and A below; then 
with 60 hours, A above and B below; then with 60 hours, B 
adove and A sbelow: And 2454 effective signals were observed 
at each station 
The result i i that the pendulums suffered no injury in their 
changes; and that the acceleration of the pendulum on being 
carricd down 1260 feet es 24 seconds per day, or that gravity is 
increased by —;,455 pa 
It does not appdar ively that this determination can be sensi- 
bly in error. The circumstances of experiment were, in all re- 
spects, extremely favorable; the only element of constant error 
seems to be that (in consequence of the advanced season of the 
year), the upper station was cooler by 7° than the lower station, 
and the temperature-reductions are therefore liable to — uncer- 
tainty which may remain on the correction for 7°. e reduc- 
tions employed were those deduced by esa from direct experi- 
ment, and their uncertainty must be very sm 
If a calculation of the earth’s mean iene were based npon 
the determination just given, using the simple theory to which 
allusion is made above, it would be found to be — six 
times and seven times the density of water. But it is 
yet to take into account the deficiency of matter in ie oc ieallery 
of the Tyne, in the hollow of Jarrow Slake, and on the sea- 
coast. It is also cess to —_ more precise determinations 
all coe iencies. It seems probable le that the resulting num- 
ber for the earth’s density will probably be diminished by t 
more accurate estimations. 
