ATMOSPHERE IN GREAT BRITAIN AND ON THE CONTINENT. 33 



was still northerly, while at high level it had just ceased to blow. About mid-day it 

 had changed to S. high up, and to S. and then to S.E. low down, and the dust at both 

 stations had begun to rise. At 12 o'clock it was 450 at the high station, while at 

 the low station it had risen from 203 at 10 a.m. to 1325 at 3 p.m., and 2200 at 6 p.m. 

 At high level also the number continued to rise after mid-day, and was over 1000 

 at 10 p.m., and continued rising till a little after 1 a.m. on the following morning, 

 when the number was 1500 per c.c. At midnight the wind had greatly increased 

 in strength, and was blowing with a force of 3, and had backed to S.S.E. After 2 a.m. 

 on the 26th the number at high level had greatly decreased under the influence of 

 the strong wind, which had still further increased and swept away the impure air. As 

 the morning advanced the wind changed to S.W., and in the afternoon it had gone 

 N. W. and fallen in force to 1 to 2. With these changes the number of particles fell from 

 1500 to 175 per c.c. 



While all these changes were taking place on the 26th at the high level, matters were 

 somewhat different at the low one. The wind, which was S.E., had changed to S.W. by 7 

 a.m. at the high station, and the number of particles had fallen ; but at the low station the 

 wind was still S.E., or the same as it was the previous night, and the number of particles 

 was still high, being 1950, or very near what it was the previous evening. When the 1 

 p.m. observations were made at low level the wind was found to have changed to the W., 

 with the result that the number of particles was now low at the low station also. The 

 number fell to 35 per c.c, which was much lower than was observed at high level on this 

 day. On the following day, the 27th, the wind went southerly at both stations, and the 

 dust increased to 1950 at the low station and 662 at the high. The following day the 

 wind was westerly at both stations, and the amount of dust fell at both. 



While these high and low level observations were being made, a record of maximum 

 and minimum temperature was kept at the low level. Observations were also made on 

 the solar and terrestrial radiation by means of a thermometer with black bulb in vacuo, 

 and a minimum thermometer placed on the grass. These observations were kept with the 

 view of seeing whether the dust in the atmosphere has any effect on the temperature 

 of the air and on the radiation, as previous observations seemed to indicate. 

 Unfortunately, owing to the climatic conditions during the period, — there being no 

 days of continuous sunshine nor nights without clouds, — these radiation records are of 

 no value, as the temperature of the air during the period was more a question of the 

 direction and force of the wind than of local influence. 



Dust and Transparency. 



During these Kingairloch observations an attempt was made to measure more 

 accurately the transparency of the air in the manner described in previous parts of this 

 paper, by estimating the amount of haze on the distant mountains. This was done with 

 a view of testing more closely the relation' between the amount of dust in the air and its 

 transparency. In order to prevent any mental bias, from a knowledge of the number of 



VOL. XXXVII. PART I. (NO. 3). G 



