ATMOSPHERE IN GREAT BRITAIN AND ON THE CONTINENT. 23 



On the morning of the 19th there was an entire change in the atmosphere ; it was now 

 clear and looked very much as it did during the previous visit. All the thickness was 

 gone ; there was nothing but a fine haze in all directions. Had anyone been present on 

 this morning who was inclined to believe in the dust-clearing effect of thunderstorms, his 

 belief would have been much strengthened by the improved and purified appearance of 

 the atmosphere after the storm. We have given reasons for supposing that the storm, 

 as a thunderstorm, had no influence on the amount of dust, and it will be seen later on 

 that the change was not due to any change in the air, but to a change of the air itself. 

 The increase in the transparency of the air on this morning was accompanied by a 

 reduction in the number of particles, which was now as low as last year. As the day 

 advanced the number gradually diminished to about 400 per c.c. The air was fairly dry 

 and very clear. Zurich, which is 25 miles distant, was visible, as well as the range of the 

 Jura Mountains to the N., while far in the E. was clearly seen Hochgerrach, one of the 

 most distant mountains seen from the Rigi, being about 70 miles away. All these were 

 seen on this morning for the first time this year. The upper atmosphere remained clear 

 during the whole day. It, however, did not remain long in this condition, as next 

 morning the air was beginning to thicken, and by mid-day there was a thick haze, and 

 the air had much the same appearance it had during the first days of this visit, and the 

 number of dust particles was again very great. 



The last of the observations made on the Eigi were taken at mid-day of the 20th, after 

 which I proceeded on my way to Lucerne. On arriving at Vitznau, at the foot of the 

 mountain, the air was tested at 3 p.m., when it was found to be very impure ; the number 

 of particles being as high as 10,250 per c.c, or much the same as it was when tested on 

 the way up the mountain. Its humidity was also much the same, and the air had very 

 much the same thick appearance. 



I was just completing these observations at Vitznau, and was about to pack up to 

 catch the boat for Lucerne, when, on looking over the figures in my note-book, I noticed 

 an unusual unsteadiness in the numbers. At first I began to fear something had gone 

 wrong with the instrument, and that the observations would require to be rejected. It 

 was, therefore, necessary before packing up to test the apparatus. On doing this, no fault 

 from leakage or otherwise could be found. There was, therefore, no reason for rejecting 

 the observations ; it was, however, thought advisable to repeat the test. When this was 

 done, it became evident that the number of particles was becoming still smaller. The 

 second test showed that the number had fallen from 10,250 to 6000 per c.c. The 

 next test gave only 3500. As usual, all these figures are from averages of ten tests. 

 Under these conditions it was difficult to get rid of the feeling that the instrument was 

 not working correctly. The rapid fall to about one-third the number of particles did 

 not add to my comfort, but again gave rise to unpleasant feelings regarding the value of 

 the observations, more especially as the next test showed the number to be now under 

 3000 per c.c. Fortunately, my discomforts were soon ended and confidence restored. 

 It was now time to take the readings of the wet and dry bulb thermometers, and also 



