192 WAVES OF SAND AND SNOW 



formed a translucent screen upon which haloes and 

 mock suns were seen in beautiful opalescence. 



The above observations bear upon the question 

 of the best form of fence for arresting drifting 

 snow. Fine drift which would be wafted over a 

 closed fence would quickly form a deposit in the 

 minor eddy spaces to leeward of an open fence. 

 Different forms of fence might ultimately collect 

 the same maximum quantity of snow, but the best 

 form would be that which collected it most quickly, 

 and this would be ojie with, so to speak, a fine mesh. 



In the late autumn I have watched the 

 drifting of the large leaves of plane -trees in 

 Londoji. As the leaf drifts some part of it is 

 generally in contact with the ground, and although 

 it is occasionally in the air its flight resembles 

 a jump or skip, the course of the leaf being, in 

 the language of golf, almost all " run " and hardly 

 any "flight." One day, with a southerly wind, I 

 saw these leaves banking up against a stone step 

 at one of the entrances on the south side of 

 Kensington Gardens. The obstruction quite 

 stopped their progress until a sufficient quantity 

 had collected to provide an inclined plane reach- 

 ing the level of the top of the step. Then, as other 

 leaves arrived, they glided up the slope, and, sliding 

 along the upper surface of the stone step, invaded 

 the gardens. 



