1892 - 93 .] Mr Aitken on Hazing Effect of Atmospheric Dust, 91 
come to it but little polluted, whilst from all other directions it 
comes polluted by its passage over more or less densely populated 
districts. 
By comparing the haze on days when the air had the same 
humidity, the relative transparency of the winds from different 
directions has been obtained, — that is, the relative transparencies of 
the air from polluted and from unpolluted areas. 
Winds from the W., N.W. and N. are more than 6 times clearer 
than the southerly winds when the air is damp, and more than 9 
times clearer when the air is dry enough to give 3° or more of w^et 
bulb depression. 
The air near Falkirk is about 10 times more hazed when the 
wind is E., S.E., S., and S.W., than it would be if there were no 
inhabitants in the country. 
The transparency of the air increases with its dryness, becoming 
about 3*7 times clearer when the web bulb depression is 8° than when 
it is 2°. That is, the clearness of the air is inversely proportional to 
its relative humidity ; or, put another way, if the air is 4 times 
drier, it is about 4 times clearer. 
The isatmid lines for Ealkirk for the different directions of wind, 
at different humidities, show that the density of the haze in our 
atmosphere is proportional to the density of the population in the 
direction from which the wind blows ; the isatmid lines for all 
humidities being closer to the place of observation the denser the 
population in the direction from which the wind blows. 
