48S 



MR A1TKEN ON ATMOSPHERIC DUST. 



Year. 



Mediterranean. 



Alps. 



Highlands. 



Atlantic. 



1S89, .... 

 1 1890, .... 



1891, .... 



1892, . 



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 



In the above table, the Mediterranean air was tested on the shore ; the air from the 

 Alps, on the Rigi Kulm ; in the Highlands, at Alford in Aberdeenshire ; whilst the 

 numbers for the Atlantic are from the Kingairloch observations. So that, though the 

 air of the Alps was tested at an elevation of 6000 feet, yet it was not as free from dust 

 as Atlantic air at low levels. If the Ben Nevis observations had been used, the contrast 

 would have been still greater. A similar result is brought out if, in place of using the 

 lowest dust readings, we use the mean numbers of the particles at the different stations 

 when the wind is blowing from the different purifying areas. These figures are entered 

 in the. following table : — 



Year. 





Mean Number of Dust Particles per c.c 



. in air coming from 





<~ 2 

 ° 2 



iff 



Mediterranean. 



5— "" 



Alps. 



<*-, 2 



it 



Highlands. 



«-< 2 

 ° 5 



Atlantic. 



1889, . 



1 



1600 



39 



698 



8 



697 



8 



481 



1890, . 



2 



767 



21 



1030 



8 



703 



65 



337 



1891, . 



7 



1865 



31 



575 



16 



401 



74 



297 



1892, . 



7 



2002 



22 



1341 



21 



468 



53 



366 



1893, . 



11 



1363 



9 



1402 



33 



605 



58 



347 



Mean, . 





1611 





892 





552 





338 



The above table shows clearly the greater purifying effect of the Atlantic area, 

 which no doubt is due to its great extent, and the amount of condensation and 

 precipitation which takes place over it. The table also shows that the air in its passage 

 across Scotland from the West Coast to Aberdeenshire gets a considerable increase in 

 the amount of its dust, and that the Mediterranean area, with its comparatively small 

 condensation and rainfall, has on an average about five times the amount of dust 

 contained in the Atlantic air. The air from the Alps cannot be compared with the 



