530 Proceedings of the Royal Society of Edinburgh. [Sess. 
hundreds of dust observations in that district, and have records with which 
to compare those taken after the passage of the comet. Kingairloch, where 
the previous observations were made, not being available, I selected Morar 
in Inverness-shire, situated 25 miles to the north-west of Kingairloch. 
Morar is fairly free from local pollution, there being only a few crofters’ 
houses near, and the smoke from their fires can be easily avoided, though 
at first, owing to some of them being hidden among low hills, they gave 
trouble, causing the number of particles observed to be irregular ; but by 
changing the position of observation cross-wind ways, one could easily get 
clear of their effects. 
Along with dust observations I made arrangements for taking observa- 
tions on the electrical condition of the atmosphere, because it was thought 
that it might possibly be affected by the tail of the comet. Observations 
on sunset colours were also to be made, and recorded by means of colour 
photographs, as it was thought that if there was an increase of dust after 
the passage of the comet the sunset colouring would probably be finer. 
Dust Observations. 
I arrived at Morar on the 13th of May to get things in working order 
and get some readings of the number of dust particles before the passage of 
the comet on the morning of the 19th. The weather conditions during 
part of the time the observations were made were not very favourable for 
the investigation, owing to the absence of any well-developed circulation, 
with the usual result, under these conditions, of high numbers being observed. 
On the 13th, when the observations began, the circulation was dominated 
by a depression situated over the English Channel. This caused easterly 
winds over our area, and as the air was drawn in from the Continent the 
number of particles was high, varying from 1250 per c.c. to 3000 per c.c. 
On the 14th the circulation was more northerly, and the number fell 
slightly, remaining under 2000 per c.c. On the 15th the number was still 
about the same as on previous day, though the local wind had changed to 
S.E., while the weather report of the Meteorological Office shows the 
general circulation to have been N.E. On the 16th the local wind was still 
S.E., though the general circulation was N.E., and the number of particles 
fell to about 1000. On the 17th and 18th, though the local wind was still 
S.E., the general circulation was slightly north of east, and the numbers fell 
to from 500 to 750, showing that the local circulation was dominated by the 
general circulation, as these figures are low for true S.E. winds in that 
district. On the 19th and 20th the general circulation began to draw 
