533 
1909-10.] Halley’s Comet and the Earth’s Atmosphere. 
passing through the open window. No attempt was made to get absolute 
measurements, though a rough approximation might be yet obtained if re- 
quired. Observations were made at frequent intervals all day, and the 
angle of divergence of the leaf noted if the electrification was weak, and 
the number of discharges per minute if it was strong. The sign of the 
electrification was also at the same time ascertained. 
When the observations began on the 13th of May the electrification was 
weak and the usual steady positive of fine weather. The fine weather con- 
ditions remained on till the 18th with but little variation. Sometimes the 
electrification was only just strong enough to enable its sign to be deter- 
mined, and sometimes the divergence of the leaf might amount to 45 or 
SO degrees, but it was never observed strong enough to discharge. The 
electrification on the 18th was the same as previous days, but on making- 
observations after 10 p.m. it was noticed that the electrification had now 
changed and was negative, but weak. This change in the electrification at 
once awakened one’s interest, as it took place within a few hours of the time 
the earth was expected to pass through the tail of the comet. One 
naturally asked, could this be the advance skirmishers of the electron 
host which some authorities thought might constitute the comet’s tail ? If 
one had only taken time to think, it would have become apparent that this 
could hardly be the case, because even supposing the comet’s tail was com- 
posed of electrons, and these had passed into our atmosphere, they could hardly 
be expected to penetrate through it and reach the earth. However, one’s 
interest being aroused, I watched the instrument for some time, and was 
rewarded by seeing the electrification rapidly increase, till at last I saw it 
discharge for the first time. It then quickened the rate of its discharge till it 
was discharging at the rate of six times a minute, the electrification being — 
all the time. It may be as well to state that the weather, which from the 
beginning of the observations had been very warm and nearly cloudless, 
had on the afternoon of the 18th shown signs of a change. Clouds formed 
in the afternoon, and the sky was quite clouded two hours before the change 
in the electrification took place. 
This change in the electrification so near the time of the earth’s passage 
through the tail of the comet seemed to promise some interesting results 
to follow, but alas ! on returning to the electroscope next morning at 4 a.m., 
while we were still supposed to be moving through the tail of the comet, 
the electrification was found to have returned to its usual settled fair-weather 
condition of feeble +, and it remained feeble till the evening, when it 
gave a display of + discharges. On the morning of the 20th the potential 
was low and + , but a short thunderstorm before 5 p.m. changed the conditions. 
