1909-10.] Halley’s Comet and the Earths Atmosphere. 
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XXXIX. — Did the Tail of Halley’s Comet affect the Earth’s 
Atmosphere ? By Dr John Aitken, F.R.S. 
Part I. 
(MS. received June 21, 1910. Read July 18, 1910.) 
The return of Halley’s Comet in May of this year gave rise to much 
speculation as to its possible effects on the earth. As it was expected that 
the earth would pass through the tail of the comet when the comet passed 
between us and the sun, many observations were arranged for in order to 
see if the tail, whatever it was composed of, had any effect on the earth 
or on its atmosphere. If the tail was composed of matter in any form, 
gaseous, or fine solid or liquid particles, then it seemed possible to get some 
evidence of its presence in the atmosphere ; or if the tail was composed of 
electrons, then these would disturb the electrical condition of the atmosphere, 
and also the magnetic condition of the earth. 
The part of this inquiry which specially appealed to me was the 
investigation of the question of the possibility of the tail being composed of 
minute solid or liquid particles. If the earth passed through the tail of the 
comet and the tail was composed of fine dust, then we would expect an 
increase in the number of dust particles in our atmosphere, which we might 
expect to find in its lower layers some time after the passage. As there are 
few observers in this particular part of meteorology, I made arrangements 
for conducting dust observations. If the observations were to be made 
with the dust-counter, it was obviously necessary that they be made in some 
isolated part of the country, so as to get free from artificial sources of dust, 
and also in a district of which we have already some information as to the 
number of particles under different conditions, as without this knowledge 
it would be impossible to come to any conclusion from merely isolated 
observations. It was suggested indeed by someone that the dust-counter 
might be used along with other means of observation in balloon ascents ; 
but as there are no previous records of observations of dust made in balloons 
in the upper air, it is evident any such observations would be useless, as 
there is nothing with which to compare them. 
For the purpose of this investigation the north-west Highlands was 
selected, because the air in that district is but little contaminated by local 
pollution, and especially because I have on previous occasions made many 
