ATMOSPHERE OF GREAT BRITAIN AND ON THE CONTINENT. 645 



evident they must be studied on the spot by experimental methods, and I hope on some 

 future occasion to have something more definite to say about them. For the present, in 

 discussing the general results of the dust observations, we must put them aside, and 

 take only the morning and evening numbers as the dust readings on these abnormal 

 days. 



Dust and Direction of Wind at Kingairloch. 



In Part II. we have seen that the purest winds at this station are those blowing 

 from the north-west quadrant; the most impure, those blowing from the south-east 

 quadrant, that is from the direction of the most densely inhabited parts of Scotland. 

 An examination of the diagrams for 1891, 1892 and 1893 fully confirm this conclusion. 

 In 1891, from the 7th to the 13th July, the winds were mostly northerly and the 

 number of particles small, except on the afternoons of the days of abnormal numbers. 

 From the 14th to the 21st the winds went south-easterly, but, as during the 14th, 

 15th and 16th, these S.E. winds were only local, the general circulation being still 

 northerly, the number of particles did not rise much. On the 17th, 18th and 19th the 

 general circulation was southerly and the number of particles became great. On the 

 20th and 21st the general circulation became more westerly and the dust decreased. 

 From the 22nd to the second last day of this year's observations the wind remained 

 northerly, and, except on parts of the days of abnormal readings, the number of particles 

 was very low. It will be noticed that there was generally rather more dust at low than 

 at high level, and that, except on a few occasions, the dust readings at high and low- 

 level rose and fell together when there were observations at both levels at the same hour. 

 It will, however, be noticed that on the 7th and 14th the numbers went very much 

 higher at high than at low level ; this was probably due to the two stations at the time 

 being in different air currents. The day previous to these high readings on the Ben, 

 the general circulation, as the arrows show, was very mixed, and at the time the read- 

 ings were taken the winds were blowing from different directions at the two stations. 



Coming to the diagram for 1892, it will be seen that from the 30th June to the 9th 

 July, the general air circulation was a little confused, with light winds generally from 

 the W. to N.W. at low level, and the number of particles was generally low. On 

 the 9th the wind went easterly and the number began to rise, but though it continued 

 easterly til] the 16th, the number was never high. This was owing to the genera] 

 circulation during the most of the period being north-easterly. From the 16th to the 

 26th the wind was generally northerly and the number of particles low, except on the 

 clays of abnormal readings. On this year also the observations at high and low level 

 follow each other remarkably closely — generally the low-level curve is the higher, but on 

 some days it will be noticed they almost coincide, as on the 16th, 17th and 18th July. 



When the observations were begun in 1893 the circulation was northerly and the 

 numbers low. In this condition matters remained from the 22nd to the 26th June. 

 At the latter date the wind was blowing in all directions over our area. A S.E. 



VOL. XXXVII. PART III. (NO. 28). 5 E 



