ATMOSPHERE OF GREAT BRITAIN AND ON THE CONTINENT. 633 



me after descending on my last visit. I happened to be busy in my room at Lucerne 

 towards sunset and had not been looking at the view nor thinking of sunset effects ; when 

 at last I looked out of the window it was not the beauty of the scenery that arrested my 

 attention, but the magnificent display of colour on the mountains and clouds, — a display 

 far beyond anything I had ever seen from the Bigi Kulm, though I had seen sunsets there 

 in all conditions of weather. 



Dust and Direction of Wind on the Rigi. 



It was found in Part II. that winds from inhabited areas always brought impure air 

 to the Kulm, and that when it blew from the south, that is from the Alps, it was pure. 

 Turning now to the last three years' observations, aided by an examination of the weather 

 charts of Switzerland, which, as before, have been kindly supplied by M. Billwiller, we 

 find that during the time of the 1891 visit the wind at the high-level stations, — namely, 

 the St Gothard and Santis, — was blowing from a pure direction on the 19th, when the 

 observations were begun, and that it continued to blow from the Alps till the morning 

 of the 24th. On that day the circulation was somewhat mixed. On the 25th, the last 

 day of this visit, the circulation again set in from the Alps. As will be seen from the 

 tables, this year was the second purest of the five, and we see that during most of the 

 time the observations were being made the wind was from the Alps, thus confirming the 

 conclusion already arrived at. 



Passing on to the 1892 observations, it will be seen from Table II. that the wind blew 

 from a more or less northerly direction from the 18th, when the observations began, till 

 the 24th, when the wind began to blow from the south. During that day the southerly 

 current did little to purify the air, but the following morning the air was pure on the 

 Rigi ; but this pure air had not descended to low level, as the observations at Vitznau 

 show about 7000 particles per c.c. On the 26th, however, it had blown all the impure air 

 away at low level, the number of particles having fallen as low as 688. On examining 

 the weather charts for Switzerland for 1892, we find a change in the Meteorological 

 Stations from which reports are sent, — the St Gothard, which was found so useful for 

 giving the air circulation to the south of the Rigi, no longer appears, its place being taken 

 by the new Observatory on Pilatus. The result, so far as our present purpose is con- 

 cerned, is far from satisfactory. The new station is too near the Rigi to be of much 

 use, and there is now no satisfactory evidence of the direction in which the air is moving 

 over the Alps. I am very glad to hear from M. Billwiller that the St Gothard station 

 will be reopened before long. 



On examining the reports from the high-level stations for 1892, it would appear that 

 the great amount of dust in the air during the days of the visit in this year was due to 

 an absence of regular air circulation over Switzerland, the wind on most days blowing 

 in very different directions at the different observatories. The winds were also blowing 

 in different directions at the different stations at low level. During this period the air seems 



