140 ROUND THE YEAR 



Over-population may be a source of many evils, but 

 it is the mainspring of Life. 



SUMMER TWILIGHT. 



June 21. This evening we were able to play bowls 

 till nearly ten o'clock. It is true that the last shots 

 were made with some difficulty. It was necessary to 

 hold a white handkerchief or even a lighted match 

 over the jack to show where it was. But the finish 

 was exciting, and we persisted till five minutes to ten. 

 At that time the north-western sky was still bright, 

 and we smoked on the terrace for a long time, 

 watching the slow fading of the light and the grada- 

 tion of the colour from amber to purple and grey. 

 Some one began to talk about the long twilight 

 of midsummer, and mentioned the well-known fact 

 that it lasts till dawn. Then an argument arose 

 about the length of twilight in different seasons of 

 the year. All were agreed that it lasts longest at 

 midsummer, but opinions differed as to whether it is 

 shortest at midwinter or at the equinoxes. I have 

 since tried to inform myself a little on this point. 



The duration of twilight can only be stated precisely 

 when a somewhat arbitrary assumption is made. 

 Twilight is light received only by reflection from 

 particles, solid or liquid, which float in the air. Hence 

 it varies according to the state of the sky. In high 

 alpine regions there may be no twilight, although the 

 sun is only a little way below the horizon. But under 

 favourable atmospheric conditions twilight lasts till 

 the sun has sunk 18 below the horizon. How long 



