NO. 17.] HYGROMETERS. 15 



meters and the thermograph, as well as the hygrometers, were placed in a 

 spacious thermometer-screen of the model of the Stevenson Screen, made of 

 wood, and resting upon fouft. wooden feet fastened into the ice below. The 

 bulbs of the thermometers WeFl^ilsa height of about 1'2 metres above the 

 ground. When the sun was ctbrnradap horizon, an extra screen kept the 

 thermometer-screen in shadow. The llw instances in which the adjustment 

 oijhe extra screen was forgotten, are noted in the remarks. As there was 

 generally a wind blowing, the thermometers were well ventilated. The screen 

 had no bottom; this was necessary in order to prevent it from being filled 

 with driving snow. The observers remark in some cases, in very cold 

 weather, that the thermometers showed a litUe lower shortly after the 

 opening of the door of the screen than before. This may be an effect of 

 radiation of heat from the thermometers, and an indication of the necessity 

 of having them protected from radiation by means of the screen. The first 

 reading of the thermometers has been taken as the true reading. 



On several occasions the thermometer-screen was in danger of being 

 carried away by the screwing of the ice, and had to be taken on board. 

 Such cases have been noted in the remarks. 



HUMIDITY OF THE AIR. HYGROMETERS. 



The humidity of the air was determined from observations made with a 

 psychrometer and a hair-hygrometer. 



The SoDERBERG thermometers mentioned above (page 13) served as dry 

 and wet-bulb thermometers. When the ship was at sea, the thermometers 

 were rotated in the whirling machine. During the drift of the Fram, the 

 thermometers stood in the thermometer-screen (described above). 



From the corrected readings of the dry and wet-bulb thermometer, the 



vapour-tension and the relative humidity were computed by means of Jelinek's 



Psychrometrical Tables. When the wet-bulb thermometer was below zero, 



its reading has been corrected, in accordance with Ekholm's recommendation, 



in the following manner before using the psychrometer tables. 



From To Corr. 



—or —11° —0-1° 



— 1-3 — 2-2 - 0'2 



