220 CAPTAIN SABINE ON THE REDUCTION TO A VACUUM 



the point of suspension, the registered divisions multiplied by 1.2 give the arc 

 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 mercuiy descending from the tube raised the level of 

 the mercury in the cistern yr^th 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 capillaiy 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 The air being then withdrawn from the apparatus until the gauge 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 bai'ometer 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 "-s^ + o-^i — 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 withdrawn, were suspended by the side of the standard thermometer : these 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 Januaiy 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 



