622 MK JOHN A1TKEN ON THE NUMBER OF DUST PARTICLES IN THE 



observation, the direction and force of the wind at the time, the temperature and 

 humidity of the air ; and as in the previous tables for the humidity, the depression of 

 the wet-bulb thermometer is given. In the second last column will be found the 

 transparency of the air at the time, and in the last column the usual remarks on 

 different points. 



Hyeres. 



The first place entered in the tables is Hyeres, in the South of France, near the 

 shores of the Mediterranean. At this place the observations were generally made on the 

 top of Fenouillet, a hill about 1000 feet high, situated at about two miles from Hyeres. 

 All the observations were made in the end of March or the beginning of April of the 

 different years. The lowest number of dust particles observed at this place during the 

 time observations were made on the five years, was 725 per c.c. on the 31st March 1890. 

 The lowest number in 1891 was almost the same, being 785 per c.c. In 1893 it was a 

 little over 1000, whilst in 1889 and 1892 it was about 1800 per c.c. The maximum 

 number observed at this station over the different years is of little value, as it was always 

 due to local pollution, brought by the wind to the hill-top from Hyeres or Toulon. 

 Though the latter town is 8 miles distant, yet whenever the wind blew from the 

 direction of that town the number of particles was always very great, going up to 30,000 

 or 40,000 per c.c. 



Mentone. 



As there is only one observation entered in Tables 1., II. and III. for Cannes, it need not 

 be further referred to. Coming next to Mentone, where the observations were made in 

 April, we find that during the five years the lowest number observed was 650 per c.c. in 

 1892. The lowest number for 1890 and 1893 was under 900, whilst in 1891 it was 1125, 

 and slightly over that in 1889. The highest numbers here, as at Hyeres, are due to local 

 pollution. Though they never went so high as at Hyeres, yet a maximum of 26,000 was 

 observed in 1890, but none of the other years shows nearly so high a maximum. This is 

 probably owing to the possibility of getting at Mentone different places for observing, 

 according to the direction of the wind, so that a site could generally be selected free from 

 local pollution, whilst at Hyeres almost all the tests were made on Fenouillet. 



Milan. 



A few observations were made on the top of Milan Cathedral. As previous experience 

 on the Eiffel Tower might have led us to expect, the numbers in a situation of this kind 

 varied greatly at short intervals. In 1891 the lowest observed was 1660 per c.c, and 

 it rose in a short time as high as 40,000, the wind being east but not strong. In 1892 

 the minimum number was slightly lower and the maximum a good deal lower. On this 



