OF THE OBSERVATIONS FOR AT MO ST II E RI C PRESSURE. 99 



Comparison of the Readings of the Aneroid and Mercurial Barometers. 



The preceding tabular results furnish the means of comparing the two barome- 

 ters, and of deducing a correction to the indications of the aneroid barometer, in 

 order to give the readings obtained from the mercurial barometer, referred to 

 32° of temperature. This correction is necessarily independent of the temperature, 

 there being no thermometric readings in connection with the aneroid : any constant 

 correction for difference of level between the two instruments is included. The 

 following table contains the corresponding readings at the same days and hours, 

 each being the mean of six observations a day. 



Table of comparison of corresponding mean readings of the mercurial and the 

 aneroid barometer, and resulting correction to the latter. 



These differences appear remarkably regular, and show that the mean monthly 

 readings of the aneroid may be relied on to one-hundredth of an inch. There 

 appears to be no tendency of a change of A depending on the higher or lower 

 reading of the barometer, nor is there any variation due to changes in temperature. 

 The correction to the aneroid readings to refer them to the corresponding readings 



1 The mean of 11 days, from Sept. 20th to 30th. 



"- The mean of 21 days, from Feb. 1st to 9th, and from Feb. 17th to 28th. 



3 The mean of 16 days, from April 1st to lGth. 



