MR AITKEN ON ATMOSPHERIC DUST. 



487 



remarkably free from dust. The following table gives a 



short abstract of Dr 1 



observations : — 













Lowest. 



Highest. 



Crossing the Atlantic, . 



. 



2,000 



4,000 per c.c. 



Near Newfoundland, . 







420 



840 „ 



Gulf of St Lawrence, . 







280 



350 



Oak Bay, Victoria, 



. 





1,000 



1,250 „ 



Santa Cruz Bay, . 







700 



4,500 



Pacific Ocean, 







245 



1,375 „ 



New Zealand, 







875 



10,250 



Australia, King George's 



Sound, 





1,000 



1,250 „ 



Indian Ocean, 







243 



1,375 „ 



Arabian Sea, 







280 



1,375 



Red Sea, 



. 





383 



490 „ 



Mediterranean Sea, 



. 





875 



2,500 „ 



Dr Fredlander also made a number of tests of the air in Switzerland, generally at 

 considerable elevations, but in most of the observations the number was over 1000 per 

 c.c, except at one or two high elevations. For instance, on the Riffelberg, at an 

 elevation of over 7000 feet, the number was generally over 1000, but on one day the 

 number fell below 900, and on another to 225 per c.c. The lowest numbers observed 

 by him were obtained during an ascent of the Bieshorn. The following table gives the 

 result of his observations : — 



Height above Sea Level. 



Number of Particles per c.c 



6,700 



950 



8,200 





480 



8,400 





513 



10,665 





406 



11,000 





257 



13,200 





219 



13,600 





157 



The last number, namely 157 per c.c, is the lowest number, so far as I am aware, 

 yet observed in Switzerland or anywhere out of Scotland. 



Professor Melander of Helsingfors has also made a special study of the dust in the 

 atmosphere. His observations were made in 1894-95-96 at Saleve, near Geneva, at 

 Biskra in the Sahara, at Torhola in Finland, at Loimola on the borders of Russia, and 

 at Kristianssund and Grip on the west coast of Norway, but at none of these places was 

 the number of particles very low. At Saleve the numbers varied from 550 to 7300, at 

 Biskra from 825 to 30,375, at Torhola from 300 to 19,280, at Loimola from 363 to 

 4128, at Kristianssund from 650 to 55,025, at Grip from 375 to 109,000. 



From my own observations taken on the Continent, it appears that the air of the 

 West Highlands is purer than at any of the other stations tested. The following table 

 shows the lowest number of particles I have observed in the air coming to the different 

 stations from what might be called the purifying areas at the different places, that is, 

 from the direction from which all the purest air at the different stations came. 



