ATMOSPHERE OF GREAT BRITAIN AND ON THE CONTINENT. 639 



its ascent it is cooled, and condensation takes place. It is well known that Pilatus is 

 cloudy when N. and W. winds blow ; now these are the very winds which are more 

 especially compelled by this range to rise to the upper atmosphere, and hence the 

 cloudiness of Pilatus with winds from these directions. 



English Channel. 



A few observations were made when crossing the Channel. They were taken at the 

 bow of the steamboat and were clear of all local pollution. On June 2nd, 1891, the 

 number of particles was 4700 : it was raining and the air thick. On the 31st May 1892 

 it was calm and thick, and the number was 7000. On the 20th May 1893 the number 

 was 8500 while near the French coast, and gradually fell to 3600 on approaching England. 

 The air where the first observations were made came off the north coast of France, while 

 that tested near England came directly up the Channel, and was therefore purer. 



Garelochhead. 



At the beginning of Table II. there are a few observations made at Garelochhead 

 in February 1892. There is nothing in them calling for special remark; the results are 

 similar to those already given for this place in Parts I. and II. The air was clear 

 and amount of dust small, with N. W. winds at the beginning of the observations, and it 

 was thick and the number of particles very high with S.E. winds at the end of the visit. 



Kingairloch. 



The next observations entered in Tables I., II. and III. are those made at Kingairloch 

 in Argyllshire. They were made about the same time of the year as those given for this 

 place in Parts I. and II. While I was observing at Kingairloch, observations were being 

 made at about the same hours at the Ben Nevis Observatory. These observations were 

 generally taken by Mr Rankin, who has given great attention to this part of the Observa- 

 tory work. On a few occasions, in Mr Rankin's absence, the observations were taken by 

 other observers. The object of these simultaneous observations at Kingairloch and Ben 

 Nevis is to get the condition of the air, as regards dust, at high and low level under 

 different atmospheric conditions. The two stations are rather far apart to be quite 

 satisfactory, Ben Nevis being about 28 miles distant in a north-east direction from Kin- 

 gairloch. The great advantage, however, of Kingairloch as an observing station is its 

 remarkable freedom from local pollution. It is doubtful if there is any place nearer the 

 high-level station that can compare with it in this respect. 



For the purpose of studying the Ben Nevis and Kingairloch observations, three 

 diagrams are given with this paper, one for each year (see Diagrams L, II. and III.). In 

 these diagrams are entered the dust observations taken at both stations, a copy of the 

 Ben Nevis observations being supplied by the Scottish Meteorological Office. In the 

 three diagrams each observation is represented by a black circle, and the successive obser- 



