WINTER ASCENTS. 



275 



Duriug tko raorniiig of thi.s day there had been a strong wind from the N.W., the velo- 

 city being between 10 and 15 metres a second from near midnight to 11 a.m. In the early 

 afternoon the wuid dropped and a balloon was sent up. It did not rise very high and its 

 motion was very irregular showuig a considerable difference of wind direction in the different 

 layers. At the tim? of ths ascent there was a slight breeze from the S.E., but the balloon 

 moved slowly to the south almost immediately on rising. It then returned and passed almost 

 overhead and travelled away to the N. The instrument was found about 1|- kilometres to the 

 N.W. of the station. The trace for the lower part of the ascent is very much blurred and 

 cannot be reduced with so much certainty as the previous records. It is almost certain, how- 

 ever, that there was only a very little inversion and that the temperature from the ground 

 to 800 metres was almost uniform. The mean gradient given in the table for the first 

 kilometre of ascent is only --06^0., and this is probably fairly near to the correct value, 

 and is what one would expect after so much wind and while the different currents 

 at different heights indicate a disturbed atmosphere. Above 1,000 metres the gradient was 

 positive and tended towards a value between '5° and "6° C. per 100 metres. 



These four records were all that it was passible to obtain from the 12 balloons sent up 

 during the winter months. They give, however, very useful information. The temperature 

 gradient found in each of the ascents is given in table 137. By applying the mean gradient 

 to the mean temperature on the ground at the time of the ascents the values given in table 

 1.38 have been obtained, and they give the average conditions in the lower atmosphere during 

 cold calm weather at the end of the winter. 



Table 137. 

 Temperature gradient in the ivinter. 



Table 138. 

 Mean vertical temperatures during the winter. 



