220 
CAPTAIN SABINE ON THE REDUCTION TO A VACUUM 
the point of suspension, the registered divisions multiplied by 1 .2 give the are 
in degrees and parts. In addition to the mercurial gauge, a mercurial baro- 
meter was suspended within the glasses, having a glass tube and cistern, the 
latter sufficiently capacious to receive, if necessary, the whole of the mercury 
in the tube; an inch of mercury descending from the tube raised the level of 
the mercury in the cistern TTzth of an inch : the scale was marked in red lines 
on the glass tube. The range of the mercurial gauge not exceeding 10 inches, 
the barometer was necessary for pressures between 10 inches and the full 
pressure of the external atmosphere. Comparing it, when suspended in its 
place, with the standard barometer of the Observatory, its indication, at about 
30 inches, was found to require an additive correction of 0.32 inch ; the 
standard being corrected for capillary action, but the barometer of the ap- 
paratus uncorrected, as the interior diameter of the tube was not precisely 
known. The air being then withdrawn from the apparatus until the gauge 
was brought in action, the barometer was found to require an additive cor- 
rection of 0.41 inch after the correction for the level of the cistern, to 
make it agree with the mean indication of the two legs of the gauge ; which 
mean was observed throughout. This barometer being only used at 14 inches 
and thereabouts, an additive correction of a32 + °- li = o.36 is applied to its re- 
gistry ; which may be presumed to give a comparative indication to the gauge 
and standard barometer within a tenth of an inch. The two thermometers 
inclosed in a sealed glass cylinder, from the interior of which the air had been 
withdrawn, were suspended by the side of the standard thermometer : these 
thermometers are numbered 2 and 3 in the subsequent tables ; the standard 
is No. 1 ; and an exterior thermometer, suspended in the free air near the 
apparatus, and at the same level as the thermometers within the glasses, is 
No. 4. 
In consequence of my absence from England, the experiments with the inva- 
riable pendulum in the apparatus were suspended until January of the present 
year, when they were resumed with the valuable assistance and cooperation 
of Mr. Thomas Glanville Taylor of the Royal Observatory, whose observa- 
tions are distinguished in the subsequent pages by his name. The invariable 
pendulum No. 12, employed in the preceding experiments, being at this time 
engaged in other determinations, I obtained permission to detain and employ 
