ATMOSPHERE OF GREAT BRITAIN AND ON THE CONTINENT. 



665 



From the above considerations the probability is, that the principal purifying areas 

 of our globe are those where most clouds are formed and most rain falls. We shall 

 now examine the tables to see if we can find any information on this subject. The dust 

 observations have been made in the neighbourhood of four great purifying areas, namely, 

 the Mediterranean, the Alps, the Atlantic, and the Highlands of Scotland. If we examine 

 Tables I., II. and III., as well as the tables in Parts I. and II., we shall see the relation be- 

 tween the purifying powers of these areas. It will be seen that the air blowing from the 

 Mediterranean is never very pure. The observations made at Hyeres, Cannes, Mentone, 

 and St Remo, show that the number of particles was seldom low and never very low. 

 Much lower numbers have been observed on the Rigi in air coming from the Alps than 

 were observed on the shores of the Mediterranean. The lowest numbers of all have been 

 observed in the West Highlands in air coming from the Atlantic, though the air that 

 comes to Afford from the Highlands of Scotland is also very pure. The following table 

 shows the lowest numbers observed in the different years in air coming from the Medi- 

 terranean, from the Alps, from the Scottish Highlands, and from the Atlantic. At the 

 foot of the table is the mean value of the lowest numbers on the five years for the 

 different purifying areas. 



Table XXIII. 



Year. 



Lowest number of Particles per c.c. observed in air coming from — 



Mediterranean. 



Alps. 



Highlands. 



Atlantic. 



i 1889 .... 

 1890 .... 

 ! 1891 .... 

 i 1892 .... 

 i 1893 .... 



1600 



725 

 785 

 650 

 698 



210 

 375 



300 

 579 

 441 



262 

 127 



94 

 168 



56 



205 

 16 

 34 

 38 

 67 



Mean 



891 



381 



141 



72 



Table XXIII. shows the lowest numbers observed at the different stations in the different 

 years, and represents the greatest purifying effects yet observed in the air from the 

 different areas. A somewhat similar result is shown in Table XXIV., in which are 

 entered the means of all the observations taken in each year when the wind was from 

 the different areas. The number of observations from which the mean was taken is 

 entered in a separate column to the left of the column containing the number of particles. 

 The means at the foot of the table, give the mean purity oi the air from the different areas. 

 These Tables are defective in so far as they give no indication, and make no allowance 

 for the condition of the air before it entered the different purifying areas ; and in Table 

 XXIV. the time element is not allowed for. Observations taken at short intervals are 

 given the same value as those made at long intervals. 



VOL. XXXVII. PART III. (NO. 28). 5 G 2 



