545 
1909-10.] Halley’s Comet and the Earth’s Atmosphere. 
where, since the passage of the comet, seems to suggest some connection 
between the two. No electrical effects have been traced to the comet, but 
may not the great amount of dust in our atmosphere account for them ? 
Leaving alone the question as to whether the electric charge is on the 
gaseous molecules or on the dust, there is a point on which I think most 
will agree, and that is, that thunderstorms always take place in densely- 
hazed air ; at least, summer thunderstorms do. I do not remember ever seeing 
one take place in clear air, but that may have been from want of observa- 
tion or lack of opportunity, as very few thunderstorms take place in the 
Falkirk district. But I have noticed at the Italian lakes, where they 
are frequent, that if a thunderstorm comes and does not clear the air, it is 
sure to return on the following day. It seemed to me that on these 
occasions the first storm only cleared the upper air, the next day it cleared 
it lower down, and perhaps on the third day it cleared it to lake level ; and 
when it did that, it did not return the following day. 
Conclusion. 
These observations show that while our atmosphere has been much more 
hazed during June and July of this year than it was fifteen years ago, 
there is nothing to prove that the tail of the comet was the cause of this 
increase in dust and haze. The only evidence against it is, that all the 
increased dust and haze were connected in some way with a change in the 
upper air, as it was only while observing in anticyclonic circulation that 
the increase was markedly greater; but there is no evidence to show 
whether or no the change in the upper air was due to the comet. If it 
was not due to the comet, then it would seem to be indicated that our 
atmosphere is rapidly getting more impure from local pollution. The fact, 
however, that the increase in dust and haze was almost entirely observed in 
anticylonic areas seems to negative this supposition, as local pollution is 
most likely to affect cyclonic areas. Whatever the cause of the increase 
may be, one thing is very evident, and that is our great ignorance of every- 
thing connected with dust and haze ; and it does seem desirable that they 
should be subjected to more systematic observation in the future than they 
have been in the past. Dust, like water vapour, is an ever-present con- 
stituent of our atmosphere ; like it, is present in ever- varying quantity ; 
and, along with it, plays an important part in meteorological phenomena. 
[Table 
