539 
1 909-1 0.j Halley’s Comet and the Earth’s Atmosphere. 
shown in the first part of this paper that this is exactly what happened 
when the Morar observations were made : air clear and dnst-free in cyclonic 
areas, and thick and dusty when near the centre of an anticyclone. 
It will be noticed from Table No. II. that during the first half of the 
period, while the dust particles were few, the air was clear, though the wet- 
bulb depression was slight, being frequently under 4 degrees ; while during 
the last half, while the number of particles was high, the air was 
hazed, though the wet-bulb depression was generally high, being sometimes 
over 10 degrees. That is, the haze was greater, though the hazing effect 
of the dust was greatly decreased by its extreme dryness ; and it will be 
further noticed that it was only on the last day of these observations, 
while the number of particles was still high, that the air became thick 
owing to the decrease in the wet-bulb depression to 4 degrees. These 
results all confirm the conclusions recorded in previous papers on the effect 
of humidity in increasing the hazing effect of dust. 
Haze. 
At the end of Part I. of this communication it is stated that it would be 
possible for me to continue the observation on dust in our atmosphere 
by observing the amount of haze at Falkirk. In a paper read before this 
Society in January 1893 it is pointed out that it was possible to make 
observations on dust without a dust-counter, and there is given the result 
of some 200 observations taken prior to the reading of the paper. As 
the first paper may be inaccessible to many, I shall here recapitulate the 
method of working. 
In previous communications giving the results of observations made 
with the dust-counter it was shown that the thickness of a haze depends 
on the number of dust particles and on the humidity of the air at the time. 
The greater the number of particles, the thicker the haze ; and the dryer the 
air with the same number, the clearer it is. It is shown roughly that if the 
air is four times drier, as measured by the wet-bulb depression, it is four 
times clearer. It results from these dust-counting observations that if we 
know the amount of haze and the wet-bulb depression we can get a rough 
approximation to the number of particles present. One result of the first 
series of observations on haze was to show that the air at Falkirk is much 
more densely hazed when it comes from the thickly populated parts of 
the country than when it comes from a direction where it is thinly 
populated. Air coming to Falkirk from all directions save from the N.W. 
quadrant comes from thickly populated parts, and it was shown that the 
