ATMOSPHERE OF GREAT BRITAIN AND ON THE CONTINENT. 631 



Rigi Kulm, 1893. 



The visit to the Rigi in 1893 was made earlier in May than any of the previous ones. 

 This was owing to the much smaller amount of snow on the Alps in the spring of this 

 year permitting the railway to the Kulm being opened sooner than usual. On the 

 morning of the 10th of May the wind was southerly, but very slight. On testing the 

 air on the steam-boat on the way up the lake from Lucerne to Vitznau, the number of 

 particles was not high, but the air became less pure near Vitznau. On the hillside at 

 that place it was very impure, owing to the absence of wind, the number being as high 

 as 10,000 at 11 a.m. On ascending to the Kulm the number at 1 p.m. was very high, 

 being 8700, due to the direction of the wind being northerly. Towards evening the 

 number gradually fell to 1500. Clouds closed in on the mountain top at 1.30 p.m., and 

 remained the whole afternoon. 



The sun rose on the morning of the 11th in a cloudy sky, and by 7 a.m. clouds began 

 to pass over the Kulm, and continued to do so all day, accompanied by frequent showers 

 of rain, sleet and hail. The number of particles was low in the morning, being 525, but 

 the north-east wind increased in force, and the number rose to 2700, and fell again to 

 441 when the wind died away in the evening. As the Kulm was in cloud, no trans- 

 parency observations were possible. 



During the 12th the weather was very unsettled from sunrise to sunset. The Kulm 

 was occasionally clear of clouds, but never for long, and great masses of clouds filled the 

 valleys in most directions, while snow- and rain-showers passed over the Rigi. In the 

 afternoon a magnificent thunderstorm was witnessed in the direction of Zurich. As the 

 wind continued on this day to blow from the impure direction with some force, the 

 number of particles rose from 690 at 7 a.m. to 5700 at 3 p.m. The number fell in the 

 evening under the influence of a change of wind to a purer direction. 



On the 13th the sun rose in a cloudless sky. The E.S.E. wind, which had been blow- 

 ing since the previous evening, seemed to have greatly cleared the upper atmosphere. 

 The lower air, however, was very thick. It will be seen from Table III. that the number 

 of particles was very high during most of this day, being as high as 13,250 at 11 a.m., 

 16,500 at 1 p.m., and 11,250 at 5 p.m., and at no time was it under 2050. The great 

 amount of dust on this day seems to have been due to the wind at high and low level 

 having been from the impure direction during the two previous days, and on this day 

 also it was from the impure direction at low level, and it changed on the Rigi. to an 

 impure direction before mid-day. Further, it was variable at the different high-level 

 stations. This day was by far the dustiest observed on the Rigi, and yet it will be 

 noticed that the transparency given in the table was not a minimum. The transparency 

 observations refer to the upper air. Under the column headed " Remarks " will be found 

 some figures giving the transparency of the air when looking in different directions at 

 high level. These figures represent the limit of visibility in miles. It will be observed 



