NO. 17.] BAROMETERS. 



The above numbers lead to the equation 



Corr. = -f 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. = + 295 0'0151 . t 16 obs. 

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

 The weighted mean of the temperature-coefficient is 0'0131 per degree 

 G. 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 + 0021 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 0'93 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 + tabular (International) reduction to 0'0131 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 + 0-11 mm. 0'099 mm. 8 obs. 



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



1 The comparisons on board gave, at 11, -f 0-094 mm. The adopted correction at 11 

 is +0-17 mm., difference O^OS mm. As the comparisons in Chris tiania 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 -f- 0'12 mm, 

 which corresponds to a temperature of 18 C. 



