1909-10.] Halley’s Comet and the Earth’s Atmosphere. 
537 
the wind was accompanied by sunshine, and, though the numbers were 
high, the air remained clear. 
From Table No. II. it will he seen that from the 29th June to the 4th 
July the number of particles remained low — once as low as 140 per c.c., 
but generally from 200 to 300 per c.c., and occasionally going up to nearly 
1000. On the 5th it was too calm to get trustworthy results. On the 6th 
a change took place ; the numbers in the morning were low, but rose after 
midday and remained high all afternoon, though very variable, being as low 
as 1000 and as high as 5000 per c.c. These high numbers were probably 
not due to sunshine, as the sky was nine-tenths clouded most of the day ; and, 
further, the high numbers did not fall at night as the sunshine high numbers 
at Kingairloch did, but remained over 3000 at the evening reading. To 
make certain of the observations on this day, sixteen different tests were 
made, each consisting of the usual five or ten tests to get the mean. The tests 
were made all through the day, some at sea-level and some on a hill 600 
feet high, and all gave high readings. Further, in the evening there was 
an opportunity for getting a photographic record of the state of the air. 
Ordinary photographs of mountains are of no use for recording haze, because 
an under-exposed photograph would show little haze on a mountain, 
while in a fully-exposed one it might be invisible. In the photograph it 
will be seen that the sun’s rays where they shone through the openings in 
