NO. 17.] 



TEMPERATURE OF THE AIR. 



473 



reasonable to ascribe the diurnal period of the temperature found in the 

 dark season to the effect of the wind. 



A similar period seems to be not uncommon at other arctic stations. 

 The range at such stations is always small, and the maxima and minima 

 may occur at different hours, indicating that other causes than the sun's 

 radiation are regulating the march of the period. Such stations that show 

 the day colder than the night are Bossekop, Lat. 69 58', December, 1882; 

 Sagastyr, mouth of the river Lena, Lat. 73 23', December, 1883 ; Polaris Bay, 

 Lat. 81 36', December, 1871; Polaris House, Lat. 78 18', December, 1872. 



The diurnal period resulting from the observations from the Fram will 

 be subjected to a fuller discussion in another chapter, where I shall discuss 

 the radiation, its effect and that of the amount of cloud and of the velocity 

 of the wind, upon the amount of the diurnal range. 



In order to find the effect of the amount of cloud upon the diurnal period 

 of the temperature of the air, I have made calculations similar to those made 

 for the velocity of the wind (p. 293 to 298). The result is shown in the fol- 

 lowing Tables. 



In all the months, except July and August, the mean temperature of 

 the 24 hours is lower with a clear than with an overcast sky. The difference 



60 



