464 
MR. BAILY ON THE CORRECTION OF 
found that the number of vibrations which the pendulum made, on his arrival 
again in London, differed by 0 97 (or not quite a second of time) in a mean 
solar day, from the number of vibrations made by the same pendulum previous 
to his departure : and various causes were assigned for (what was called) so 
great and so singular a discordance * : for, I believe, at that time the results 
with the invariable pendulum were considered almost as infallible. It is true 
that we have a few instances of a contrary nature, where the pendulums, on 
their return home, have told precisely the same story as they did when they 
were sent off ; and, in the case of the two pendulums that were taken out by - 
Captain Sabine, their coincidence during the whole of the voyage was very re- 
markable, since the greatest variation from the mean did not exceed 0-32 at 
any one of the stations t ; but, these I consider rather as singularly favourable 
circumstances in his particular case, than as tending to invalidate the results 
of other experiments. In the voyage of Captain Freycinet, who took out 
three separate pendulums, we find a variation in the difference between them, 
amounting to several seconds in a day. Thus, at the Isle of Guam the differ- 
ence between pendulums No. 1 and No. 2 was 1180T62 vibrations ; whereas 
at the Isle of Rawak the difference was only 1 1 73‘693 ; being a variation of 
6’469 vibrations. At the Isle of France the difference between pendulums 
No. 2 and No. 3 was 1012‘326 vibrations ; whereas at the Isle of Rawak, the 
difference was only 1008 , 557 ; being a variation of 3 - 769 vibrations. And at 
the Isle of France the difference between pendulums No. 1 and No. 3 was 
164‘948 vibrations; whereas at the Isle of Guam the difference amounted to 
169’833 ; being a variation of 4 - 885 vibrations in a mean solar day £. Captain 
Duperrey also, who took out two of these same pendulums (No. 1 and No. 3) 
in a subsequent voyage found the difference between them, at the Malouine 
Islands, to be 169’931 vibrations ; whereas on his return to Paris the difference 
was only 168’235 ; being a variation of l - 696 vibration §. Now, in all these 
cases there ought to be little or no variation in the difference between any two 
of the pendulums : neither would there be if we could insure the making of 
the experiments precisely under the same circumstances ; and no blame can 
* Phil. Trans, for 1823, page 287. f Account of Experiments, &c. page 189. 
; Voyage autour du Monde, par M. Freycinet, (Observations du Pendule,) page 22. 
§ Connaissance des Terns for 1826, pages 294 and 300. 
