ATMOSPHERE IN GREAT BRITAIN AND ON THE CONTINENT. 31 



of the abnormal afternoon readings already referred to, the amount of dust was small, 

 and wind northerly or westerly. On the 11th the number was high at both upper and 

 lower stations, owing to the general circulation being light and irregular. On the morn- 

 ing of the 12th the number of particles was still very high, but before mid-day the wind 

 went to the W. of S. and cleared away the dust. The wind remained westerly 

 during the 1 3th, 1 4th, and morning of the 1 5th, and during these days the dust remained 

 very low. On the afternoon of the 1 5th the circulation became irregular, and the number 

 of particles great. On the 16th there was much dust in the air, partly owing to a mixed 

 air circulation and partly to the wind being E. of S. The wind changed on the after- 

 noon of the 16th to N.W., and the amount of dust fell greatly. On the morning of the 

 17th the S. wind was again blowing in the early morning, and the amount of dust had 

 increased, but it again fell in the afternoon under the influence of a N.W. wind. On the 

 18th there was little dust, and the circulation was slight from the N. The wind on 

 the 19th changed to E., and the dust increased greatly, but fell on the 20th, and remained 

 low till the 25th, owing to a N.W. wind which blew during all these days. On the 

 afternoon of the 25th the dust rose under the influence of a S.E. wind, but fell on the 

 following day, when the wind went W., but rose again on the 27th owing to easterly 

 wind, and fell on the 28th, the air on that day coming from a westerly direction. These 

 results confirm the conclusions arrived at in Part I. 



During the time these observations were being made at Kingairloch, the weather was 

 frequently disturbed by depressions which passed across the United Kingdom, and gave 

 rise to very unsettled conditions ; but on the 20 th an anticyclone approached our 

 islands from the W., and the conditions remained fairly steady till the afternoon of the 

 25th. During all these days the isobars were regular, and kept their direction constant, 

 and the wind blew steadily from the same point. From an inspection of the table and 

 diagram it will be seen that the wind on these days blew steadily from the N.W. This 

 N.W. wind rapidly swept the impure air away, and during the five and a half days it 

 blew the number of particles was very low, — on two days excessively low, — and remained 

 low till the direction of the wind changed. 



A comparison of the number of particles at low level at Kingairloch and on Ben Nevis 

 shows that though there is considerable resemblance in the figures at the two stations, yet 

 the likeness is not very close (see diagram). We could not expect otherwise, as the con- 

 ditions are so different at the two stations. The day maximum of dust on most days at 

 high level interferes greatly with the parallelism of the two sets of observations. Further, 

 the effects of the force of the wind on the number of particles is not the same at high 

 and low level ; and, again, the winds are often different at the two stations. As a 

 rule, however, when the numbers were high at the low level they were also high on the 

 Ben, and when low at low level they were low on the Ben. On the 1st, 2nd, 3rd, 4th, 

 11th, 12th, 19th, 25th, and 26th, the numbers were high at Kingairloch, and on the Ben 

 they were also high. On the 5th, 7th, 10th, 20th, 21st, 22nd, 23rd, 24th, and morning 

 of 25th, they were low at both stations. Between the 12th and 18th only two high- 



