THE DUST OF THE AIR 



ONE of the flies in the ointment of Summer is the dust. 

 It blinds and chokes us, making the highway journey 

 a penance ; it disfigures the hedgerows and spreads into 

 the meadows. Sometimes it rises in beautiful swirling 

 pillars which glide like wraiths along the road ; but, except 

 at a distance, dust is an abomination, and in many parts of 

 the world it is a terror. In the present transition age of 

 means of locomotion it is distressing to see how the dust 

 raised by automobiles has ruined beautiful wayside gardens ; 

 let us hope, however, that just because of motor-cars we 

 shall eventually have less road-dust than ever. 



" Except at a distance," we said, for it is well known 

 that dust plays a very important role in making the world 

 beautiful, and it is well to consider this side of it. The 

 fundamental investigations, we believe, were those made a 

 good many years ago now by Dr. John Aitken, who first ex- 

 plained clearly the making of mist and the secret of fog. 

 Mist is a concentration of moisture round the dust particles 

 of the air, which are carried up from the earth's surface by 

 currents, by evaporation, and by volcanic action, or are 

 due to meteorites. Fog, in the same way, was shown by 

 Aitken to gather round the same minute foci ; and even the 

 raindrops have their black hearts. It is interesting to 

 look with a strong lens at the minute motes formed on the 

 well-cleaned glass-cover of a museum case during a foggy 



day ; one sees that an almost microscopic drop has fallen 



229 



