1889 - 90 .] 
Mr J. Aitken on Dust Particles. 
199 
The Baveno observations were made in similar weather to those 
of Bellagio, that is with little wind on most days, and the air damp 
and generally very thick, due to an accumulation of local impurities. 
The only occasion on which a low number was obtained here was 
on the afternoon of the 16th May. This pure air was found at 
some distance from Baveno, at the entrance to the Simplon Pass, 
above all the villages near the lake. The wind was light, but it 
descended from the mountains and was pure ; owing however to the 
imperfect mixing of the hill and valley airs, the numbers varied a 
good deal. As will be seen from the table, they varied from 546 to 
850 per c.c. 
On the 18th of May the air was tested at Locarno, at the head of 
Lake Maggiore. The place selected for observing was on the hill- 
side above the pilgrimage church of Madonna del Sasso, about 600 
feet above the lake. The wind was northerly, that is from the 
mountains, and the air was fairly pure, only 1300 per c.c. There 
was thunder at the time, and there had been heavy showers all day. 
The Rigi Kulm Observations. 
Being desirous of making some observations on the air at the 
top of mountains, the Bigi was selected as the most suitable for 
the purpose, on account of its elevation and isolated position. The 
convenience of being able to live at the top was another recommen- 
dation, as one would always be in a position to take advantage of 
any meteorological change which might take place. In all these 
respects perhaps Mont Pilatus would have been a better place for 
the purpose, as it is more isolated and is 1000 feet higher, but at 
the time of my visit the railway was not finished, and there was a 
difficulty in getting up apparatus and luggage sufficient for a visit 
of some days. I found the Bigi Kulm hotel a very convenient and 
comfortable place for observations of this kind. The hotel is so 
near the top of the hill, that on any change taking place one can 
be at the top in a minute or two and have a clear view all round, 
and the dust-counting apparatus can be placed in such a position 
that it tests the true passing air from whatever direction the wind 
may happen to blow at the time. 
As the Bigi observations will probably be the most interesting, I 
have entered in the table the results of most of the tests, and later 
