ATMOSPHERE IN GREAT BRITAIN AND ON THE CONTINENT. 29 



Before going further, I wish to call attention to a few of these Kingairloch observations 

 that are so exceptional that it is difficult to put a value on them. It will be noticed that 

 on the afternoons of many of the days the numbers, which had been low in the morning, 

 became very great. When the afternoon observations of July, made on the 3rd, 4th, 6th, 

 7th, 11th, and 15th, are examined, it will be seen that the numbers were much higher than 

 they were in the morning ; also that they were very high for the direction of the wind. 

 All previous experience has shown that winds from uninhabited districts are pure. 

 These afternoon observations, however, stand out as marked exceptions to this rule. 



It cannot be said that any very satisfactory explanation has been found of these 

 abnormal readings, though the following considerations show how they may possibly be 

 accounted for. For the purpose of studying these Ben Nevis and Kingairloch observa- 

 tions, the diagram given with this paper has been prepared. In the diagram are entered 

 the dust observations taken at both stations from the 1st to the 28th July. The observa- 

 tions taken on Ben Nevis were made by Mr Eankin, a copy being kindly supplied to 

 me by the Scottish Meteorological Office. Each observation is represented in the 

 diagram by a black spot, and the successive observations are connected by straight 

 lines. The Kingairloch observations are represented by large spots and connected 

 by thick lines, while the Ben Nevis observations are represented by smaller spots and 

 connected by finer lines. These irregular lines may, for convenience, be called dust 

 curves, and their rise and fall indicate the variations, from time to time, in the amount of 

 dust at the two stations. 



At the top of the diagram is entered a series of arrows representing the direction and 

 force of the winds on Ben Nevis at the hours the observations were made ; and at the 

 bottom another series of arrows representing the winds at Kingairloch. Then, as the 

 amount of dust at these stations would probably depend on the general circulation of the 

 air over the area of the British Isles, a study of this was made from the weather charts 

 kindly supplied to me by Mr Scott of the Meteorological Office, London. The result of 

 this investigation is given in the diagram, being shown by a third series of arrows. The 

 series of arrows indicating the general circulation are placed between the upper series 

 indicating the Ben Nevis winds, and the lower series showing the Kingairloch winds. If 

 the general circulation was regular over one area, and the winds blew in one direction at 

 all places, then one arrow is sufficient to represent the conditions ; but when the circula- 

 tion is mixed, blowing from one direction at one place, and from another direction or 

 directions at other places, then two or more arrows are required. By examining this 

 series of arrows for any date, it is at once seen whether at the time the general air cir- 

 culation was regular or irregular over one area. 



Further, on examining the meteorological weather charts it is seen that, whenever the 

 isobars were wide and irregular, the winds were various and variable, and that they blew 

 with but little force. On considering what the effect of these conditions would be, it seems 

 probable that on the days when the general circulation is confused and light, we cannot be 

 certain of the source of the air we are testing ; while we are working in a northerly wind 



