RELATION OF WIND TO TOPOGRAPHY 



553 



As my object was principally to find out the influence of wind in the 

 layers near the surface or those which carry the greatest quantity of 

 sand and come into contact with the lowest strata of the vegetation, I 

 did not have the sand separator arranged to receive sand which was 

 lifted higher than 8 cm. above the surface. 



It seemed, further, to be of considerable interest to know how 

 great the difference of the velocity of wind was on level and broken 

 ground, and consequently to what extent a rough surface influenced 

 the movement of sand. On a vacant lot, south of Fremantle, where 

 the sand had been covered with a layer of loam for agricultural 

 purposes, I had opportunity to make some observations in that 

 direction, and subsequently I measured the surface velocity of air on 

 a grassy plot adjoining a field of drifting sand. 



Day after day the experiments were continued under different con- 

 ditions of wind and humidity, and with the aid of an assistant I was 

 able to make careful observations of the tactics of the moving sand, 

 and to secure some results which are not without interest. 



Velocity of wind. — Of the hourly registrations made, those for six 

 days will be given as samples. The place of observation was on an 

 open beach, 40 m. from shore. Angle of sloping about 12°. The 

 following table indicates the result. Velocity in meters per second. 



VI 



7 A.M 



8 



9 

 10 

 II 

 12 



I P.M.. 



2 



3 



4 

 5 

 6 



10.4 

 10.9 



II-5 

 14.2 



15-7 

 18.6 

 18.9 

 17 .2 

 18.4 

 20.2 

 19.7 

 16. 1 



Result of experiments on carrying capacity. — A few of the observa- 

 tions made will here be given to show the details obtained. The 

 Roman numerals refer to corresponding days in the table of velocities. 



I. No drifting was observed in the forenoon. Slight movement 

 was noticed between i and 2 o'clock. During the next hour the sand 



