4 H. MOHN. METEOROLOGY. [NORW. POL. EXP. 



between the wake and the keel was continually observed from the taffrail, and 

 has been taken into account in the determination of the ship's true course. 

 The total error of the compass (declination -f- deviation) has been taken 

 from Professor GEELMUYDEN'S Tables, D, E and F, in his memoir, Astronomical 

 Observations, vol. II of the present Report, No. 6, pp. 7082. 



ATMOSPHERIC PRESSURE. BAROMETERS. 



For the observation of atmospheric pressure, the Expedition had three mer- 

 curial barometers, of which one was used as a standard and controlling baro- 

 meter, and the other two were used for the regular, daily observations. 



A series of comparisons between these barometers and the standard 

 barometer of the Norwegian Meteorological Institute was made in 1893, from 

 March 15th to May 23rd. The number of comparisons was 16. The height 

 of the mercury-column varied from 731 mm. to 776 mm., and the reading of 

 the attached thermometers from 4 to 17 C. The observations were reduced 

 to by means of the International Meteorological Tables. 



I. The Standard Barometer was of the Wild-Fuess construction, and 

 was designated as Fuess No. 362. 



Its correction to true barometric height was found, in 1893, to be 

 -f- 0'088 mm. The mean deviation (M. E.) of a single comparison from this 

 mean was + 0'042 mm. The deviations did not indicate any appreciable 

 change of the correction with pressure or temperature. 



In the beginning of 1895, the tube of this barometer was broken, and a 

 spare tube sent with it from the maker was inserted instead of the broken one. 



In March, 1897, after the return of the Expedition, Fuess No. 362 with 

 the spare tube was compared with the standard barometer of the Meteoro- 

 logical Institute, and -f- O'lO mm. was found as the most probable constant 

 correction. The barometer was not then in such good working-order as in 

 1893. The constant correction adopted is -f- 0'09 mm. 



During the comparisons made on board the Fram, Fuess 362 was 

 suspended in the cabin. 



II. The Kew Station Barometer Adie No. C 763 was used during the 

 drift of the Fram in the ice. 



