1892 - 93 .] Mr Aitken on Hazing Effect of Atmospheric Dust. 83 
Another point which is very evident in Table No. I. is the great 
difference in the transparency of the wind from the different direc- 
tions. With W., N.W., and N. winds the air is very clear, whereas 
from all the other directions it is very much hazed. All winds from 
E. by S. to S.W. are nearly ten times more hazed than those from 
the N.W. quadrant. Table No. II. shows this very clearly. In this 
table will he found, as in the previous one, vertical columns, in 
which are entered the observations for the different depressions of 
the wet bulb thermometer; in this table are given, in the top 
row of figures, the mean limit of visibility for all the winds from E. 
to S. and S.W. for each degree of wet bulb depression, and in the 
lower row of figures is given the mean limit of all the observations 
when the wind wms in the N.W. quadrant. In this table it has 
been thought advisable to omit all the observations taken when the 
wind was N.N.E., N.E., and E.N.E., as well as those when it was 
W.S.W., because winds from these directions are not entirely from 
either polluted or unpolluted areas, and also because the observa- 
tions of haze in winds from these directions are unsatisfactory, for 
the reasons already given. The figures in Table No. II. show that 
when the wet bulb depression is 2°, the air from the N.W. quad- 
rant is about 6*2 times clearer than the air coming from the other 
directions ; and that when the air was drier than gave more than 2° 
depression, the mean of all the observations shows that the air from 
the N.W. quadrant was more than 9 times clearer than that from 
the other directions. That is, the table shows us that the air from 
densely inhabited areas is so polluted that it is fully nine times 
more hazed than the air that comes to us from the thinly inhabited* 
districts. Allowing for some pollution that must be thrown into 
our atmosphere in its passage over the N.W. quadrant, we may 
say that, in a rough way, when the wind is easterly or southerly, 
the atmosphere at Falkirk is about ten times thicker than it would 
be if there were no fires and no inhabitants. 
It will be noticed that by the method of working adopted in this 
investigation the effects of the moisture in hazing our atmosphere 
have been eliminated, and only those due to the number of dust 
particles are shown. It should, however, be noticed that if these 
observations had been treated in a manner in strict conformity with 
our knowledge of the effect of moisture in causing haze, we ought 
