1889 - 90 .] 
Mr J. Aitken on Dust, Particles. 
201 
mixed masses of the impure air of the valleys to the hill top. In 
the afternoon the wind fell a little, and the numbers were more 
constant, varying from 600 to 850. 
The observations made on the 24th show the air on the morning 
of this day to have been much the same as it was the previous 
afternoon. The wind had fallen still further, and the number 
recorded between 10 a.m. and 11 a.m. varied but little, being from 617 
to 685, showing a more uniform condition and a lower average than 
the previous day. At 4 p.m. the number had decreased to about 
400, and by 5 p.m. the number tended to increase and become the 
same as it was in the morning. 
The next day, the 25th, being the last day of my visit to the 
Rigi Kulm, I determined to make a number of tests on my way to 
Lucerne. Between 9 a.m. and 10 a.m. observations were made on 
the top of the mountain. The number observed was fairly constant, 
varying from 532 to 580. The wind was still blowing from a 
southerly direction, but not strong. On descending to Vitznau on 
the lake, I at once proceeded to make observations on the air at this 
level. The result at first somewhat astonished me, as the tests 
gave only about 600 per c.c. On examining the conditions, I 
noticed that the wind had greatly increased in force, and at this 
situation was blowing in strong gusts, and it did not come down the 
lake but came over the shoulder of the Rigi, and struck direct down 
on Yitznau, and spread out fan-like from the village as a centre. 
On each side of Yitznau the wind blew from the village, and on the 
lake in front it was off shore, so that the air tested at Yitznau 
had come from near the top of the mountain and would be much 
the same air as that tested in the morning at the top of the hill. 
Leaving Yitznau I took steamer for Lucerne, and again tested the 
air, selecting for the purpose a position on the lake side about a 
mile up the lake and to the windward of the town. The number 
observed here was but slightly increased from what it was at 
Yitznau, being only about 650 per c.c. At this situation also, the 
air came direct from the mountains to the place of observation with- 
out local pollution, as it was driven down the lake by a strong wind, 
and came to the instrument from off the water, so that unless from 
a passing steamer there was no chance of pollution. The air was 
again tested in Lucerne at the open window of the hotel overlooking 
