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



In this manner, the observations in which the wet-bulb thermometer was 

 below and above 10 are employed as well qualified to give trustworthy 



results. 



The Expedition had two hair-hygrometers, designated in the Meteorolo- 

 gical Journal as I and II. They were placed in the thermometer-screen close 

 to the psychrometer, and were read constantly during the time in which the 

 temperature of the air was below zero. The values found for the relative 

 humidity, from the observations of the psychrometer, when the wet-bulb 

 thermometer stood between and --10, served for finding the corrections 

 of the hair-hygrometer. 



The first autumn was an exception to this rule. On October 11, 

 1893, the screen was set out on the ice with its thermometers and a hair- 

 hygrometer. Before this date, no observations of the hair-hygrometer had 

 been made, but only psychrometer-observations. These, from the 2nd 

 October, were taken in temperatures generally lower than 10. In order 

 to render them serviceable for the determination of the humidity of the 

 air, I had recourse to the direct comparisons between the psychrometer and 

 the hygrometer made during the spring and autumn of 1894. The result of these 

 comparisons was that the psychrometer-readings computed in the above- 

 named manner from the psychrometrical tables, gave too low values for the 

 humidity. The corrections for the psychrometrical relative humidity found were, 

 at 10 Corr. = 0, at 20 Corr. = + 14 %, and at 30 Corr. = + 26 /o, 

 practically proportional to the temperature. The values for the humidity 

 entered in the Tables for the days from the 2nd to the llth October, 1893, are 

 computed by means of these corrections. 



The corrections found for the readings of the hair-hygrometers by means 

 of psychrometrical observations (ps), or by keeping them in saturated air (sat), 

 were as follows: 



Hygrometer I, from October, 1893, to March, 1895. 



1893. Oct. 27. Corr. +3-4% (ps). In the saloon. (Psychr. not ventilated) 

 Nov. 7. 6'9 - (ps) On board (in the chart-house?) 



