THE MICROBES OF THE AIR 



261 



on the number of dead or inorganic particles con- 

 tained in the air. Mr. J. Aitken, F.R.S., 1 has in- 

 vented an ingenious apparatus by which the number 

 of dust particles in the atmosphere may be readily 

 estimated. Among the results obtained are the fol- 

 lowing : 



No. of Dust Particles in Air. 



These results indicate that ' there is most dust in 

 the air during dry weather, and perhaps during 

 anti-cyclonic conditions, and least during wet 

 weather, and perhaps in cyclonic areas.' 



Aitken has also ascertained the minimum and 

 maximum number of dust particles per cubic centi- 

 metre (cc.) in the air of various towns, etc. Among 

 these results are the following : 



At Hyeres (near Toulon), . from 5000 to 46,000 



1 Transactions of Royal Society of Edinburgh, vol. xxxv. 

 p. 1 ; Proceedings of Royal Socie.ty of Edinburgh, vol. xvii. 

 p. 193, and vol. xviii. pp. 39 and 259. 



