1889 - 90 .] 
Mr J. Aitken on Dust Particles. 
235 
pared. At the bottom of the diagram are the dates on which the 
observations were made, and underneath the date is marked whether 
the station was in a cyclonic or anticyclonic area, A. indicating anti- 
cyclonic, C. cyclonic, and ? indicating that it could not be said to be 
in either the one or the other. In the diagram is shown the number 
of particles observed on each day. Each observation, given in the 
table referred to in a previous part of this paper, is indicated in 
the diagram by a small circle, the height of the circle above the 
base line indicating the amount of dust on the date, the scale 
being shown on the right hand side of the diagram. These dust 
observations are all connected by means of a dotted line. It will 
be noticed that in a general way the numbers were least in cyclonic 
areas. 
Plate No. 2 illustrates the same thing for the Alford observa- 
tions. Here the circulation was anticyclonic for the first four days, 
and the number of particles was high. A cyclone passed on the 
9th, and the number fell to about one-third. The circulation was 
doubtful on the 10th and 11th, but on the following days it was 
generally anticyclonic, but it will be observed that the numbers 
were low during the beginning of this period. A curious point was 
the great increase which took place on the 16th. The number in 
the morning was 1125, but it rapidly increased during the day, and 
rose to 5700 in the afternoon. In connection with this it may be 
interesting to note that on the previous day the centre of the anti- 
cyclone had passed over this station, and on the 16th lay imme- 
diately to the east of it. 
Taking now the Dumfries observations, which are shown on 
Plate No. 3, it will be noticed that the relation between the 
dust and the barometric distribution was more marked than in the 
previous cases. The circulation was cyclonic on the following 
dates — October 29th, 30th, 31st, November 1st, 2nd, 5th, 6th, and 
15th, on all of which dates there was little dust. On only other two 
days was there little dust, namely, on the 25th October and 9th 
November. On these days the number was low and circulation 
anticyclonic. The high numbers were all got in anticyclonic or 
complicated areas. 
Now comes the question, What interpretation are we to put on 
these facts? If the anticyclonic areas have more dust in them than 
