476 
MR. BAILY ON THE CORRECTION OP 
the tube. When the air is exhausted from the tube, I have, in computing the 
corrections for temperature, added 0’75 to the mean of the thermometers, to 
compensate for the effect produced on the thermometers by the removal of 
the pressure of the atmosphere ; as indicated by Captain Sabine in the Philo- 
sophical Transactions for 1829, page 214: this being the amount by which 
these thermometers were also affected by such removal. In the detail of the 
experiments, inserted in the Appendix to this paper, the readings of the ther- 
mometer are given, without this correction. In recording the barometer, the 
correction for capillarity is always included : but when the vacuum tube is 
exhausted, a syphon gauge is employed to indicate the pressure of the atmo- 
sphere, and no correction is required. 
The subjoined Appendix consists of two Tables, in the first of which is given 
a detail of all the particulars (copied from the Observation-books,) requisite 
for deducing the corrections : and in the second of which is given the amount 
of those corrections under their respective heads. Table I. shows the time of 
the first and the last coincidence ; the magnitude of the arc of vibration and 
the height of the barometer at those times respectively; the highest and lowest 
readings of the two thermometers, and the daily rate of the clock during the 
interval of each experiment : the number and date of which are always 
annexed. Table II. contains 1°. the corresponding number of each experi- 
ment in the preceding Table, for the sake of a convenient reference : 2°. the 
total interval of the experiment : 3°. the number of coincidences (minus unity) 
that have occurred : 4°. the mean interval expressed in seconds of the pendu- 
lum clock: 5°. the amount of the corrections for the arc, the thermometers, and 
the daily rate of the clock : and lastly the number of vibrations, N' or N", 
(according as the experiments were made in air or in vacuo,) in a mean solar 
day, exclusive of the correction for the pressure of the atmosphere, which is 
the quantity sought in the present inquiries. In the latter part of this Table, 
however, viz. from experiment 205 to 230 both inclusive, the correction for the 
barometer is added, and the last column then contains the true number of 
vibrations in a mean solar day, including the correction for the pressure of the 
atmosphere: for, these experiments are of a totally different kind, and are 
inserted to show the effect produced merely by reversing the face of the pen- 
dulum, as alluded to in page 40/. 
