RECORD AND REDUCTION OF THE OBSERVATIONS FOR ATMOSPHERIC 



PRESSURE. 



INTRODUCTORY REMARKS. 



The observing hours are the same as those for the other meteorological observa- 

 tions, that is, in part at equal intervals of two hours, and in part at intervals of 

 four hours. There are two records, one of the aneroid readings, the other of the 

 readings of the mercurial barometer. 



The series of observations by the aneroid is continued throughout the cruise; the 

 mercurial barometer was used only between September 20, 1857, and April 10, 



1858. The readings in the month of July and August, 1857, and of September, 



1859, are given in the record, but are not further introduced in the discussion, 

 since the ship was then rapidly changing her position, not permitting a combination 

 of the daily observations. 



The mercurial marine barometer, Adie No. 208, was compared with a standard 

 instrument at Kew both at departure and after return. The comparisons for index 

 correction are as follows (communicated in a letter from Captain McClintock, dated 

 London, December 12th, 1860) : — 



Corrections to be allied to Barometer by Adie No. 203 (or No. 407, private 



mark op the makers.) 



Before Embarkation in the Fox. 



At inches. Correction. 



30.5 +0.005 



30.0 +0.006 



29.5 +0.007 



29.0 +0.007 



28.5 +0.007 



28.0 +0.008 



Subsequent to its Return. 



At inches. Correction. 



30.5 +0.008 



30.0 +0.008 



29.5 +0.007 



29.0 +0.006 



28.5 +0.005 



28.0 +0.005 



This mercurial barometer had been used by Professor Piazzi Smyth at Teneriffe, 

 and is highly thought of by Admiral Fitzroy, in whose office it is now in use. 



It is specially stated in the reduction whenever the above correction was applied. 

 Comparisons of the readings of the mercurial and aneroid barometers will be found 

 in the discussion. 



The cistern of the mercurial barometer was four feet above the level of the sea 

 (in reference to the position of the aneroid, no statement is given). Tlic barometric 



