240 Proceedings of Royal Society of Edinburgh. [sess. 1 
For investigating whether the amount of dust in the air has any 
influence on its temperature while the sun is shining, the only 
observations illustrating the point are those made at Kingairloch in 
July; the others made in September, October, and November, 
when the sun was low, shew no marked effect from its rays. When 
we examined the Kingairloch observations, we were struck by the 
marked relation shown between maximum temperature and the 
amount of dust. It will be observed that the curve of maximum 
temperature shows four maxima, and that the dust curve has also 
four maxima, and that three of these maxima of dust happen on the 
three days of maximum temperature. On the 4th, 9th, and 13th it 
will be seen both dust and temperature were above the average. The 
same thing though not so marked, may be noticed in the Alford 
observations. At the beginning of the observations both dust and 
temperature were high; both fell towards the end, and just at the 
finish both rose again. 
These considerations point to a connection between the amount of 
dust and the temperature ; the greater the amount of dust the higher 
was the maximum temperature. But what explanation are we to put 
on this? Is it a case of cause and effect? or are both due to one cause ? 
or is it merely a coincidence ? One would have expected that the 
phenomena are far too complex for any such effect to show out so 
clearly as it seems to do in these records. Amongst other influencing 
causes besides dust, there is the wind. The force of the wind does 
not seem to assist in explaining the agreement between the dust 
and the temperature curves in these cases ; the direction of the wind, 
however, seems to have some effect. For instance, the wind was 
somewhat southerly with the high temperatures, but southerly winds 
at these stations are generally accompanied with much dust, while the 
northerly ones have a lower temperature, and little dust. This, how- 
ever, does not dispose of the whole question, as the greater or less 
dust in the different winds may be in part the cause of the difference 
in their temperature. We do not find any influence of the dust on the 
maximum temperature in the Dumfries observations; when the sun 
is low, the direction of the wind seems to be the principal influencing 
cause. Most of the high temperatures occurred with southerly to 
westerly winds. 
Humidity, no doubt, will have a powerful influence on the 
