NO. .] BAROMETERS. 



The above numbers lead to the equation 



Corr. = + 0-337 - 0'0127 t + 0-0012 (760 - 6) mm. 

 The last term becomes, when 6 = 730, -(- 0'04 mm. 



- 6 = 780, 0-02 - 



The correction may be taken as independent of the barometric height. 

 In 1893 we had Corr. = + 0'295 0'0151 . t 16 obs. 

 . 1897 - - - = + 0-337 - 0-0127 .t 86 - 

 The weighted mean of the temperature-coefficient is - 0131 per degree 

 C. The correction at is greater by 0'042 mm. in 1897 than in 1893. 

 The mean, which I have adopted, is -\- 0'32 mm. It differs from each 

 of the two values by only 0'021 mm., which is practically insignificant. 1 

 The station barometer Adie 763 was used for the current observations 

 from noon, October 12, 1893, to 7 p. m. August 14, 1896. The height of 

 its cistern above the level of the sea was - 93 metres. The reduction of the 

 height of the mercury to sea-level can be taken as -}- 0'09 mm., with no error 

 exceeding 0'05 mm. for any pressure or temperature of the air. 



The observations taken with Adie 763 have been reduced to the true 

 height of the mercury at and to sea-level by the Correction 



+ 0-32 -f tabular (International) reduction to 0131 t + 0'09 mm. 

 Reduction at = + 0'32 + 0'09 = + 0'41 mm. 



III. The Marine Barometer Adie No. C 764, was used when the 

 Fram was in open water. 



The 16 comparisons in 1893 at the Institute gave, for 2 groups, 

 Att. Therm. Corr. M. E. 



5-2 -f Oil mm. + 0'099 mm. 8 obs. 



13-3 0-14 - + 0-079 - 8 



1 The comparisons on board gave, at 11, + 0'094 mm. The adopted correction at 11 

 is + 0'17 mm., difference 0'08 mm. As the comparisons in Christiania were made 

 under much more favorable circumstances than on board the Fram, I have adopted 

 the above-mentioned value, + 0'32 mm. The check obtained by the observations on 

 board may be considered very satisfactory. The Kew correction was + 0'12 mm, 

 which corresponds to a temperature of 18 C. 



