DESERT SAND-DUNES 73 



be so great wherever I went that I wondered if 

 it could be akogether a mechanical effect. There 

 is a current opinion that when the atmosphere is 

 electrified, wind moves sand much more freely than 

 at other times, the material going into suspension 

 and remaining suspended to an unusual degree. I 

 therefore tried in the laboratory the effect of elect- 

 trifying sand, and was much struck with the great 

 mobility which it acquired. It has occurred to 

 me that sand-dunes where the underlying ground 

 is moist, being well " earthed," would be less sus- 

 ceptible to the effects of electrified wind. My 

 cousin the late Mr. E. A. Floyer, Inspector of 

 Egyptian Telegraphs, informed me that in the dry 

 desert, on the other hand, the insulation is so good 

 that it is often difhcult to get an " earth " when 

 it is required for sending a telegraphic message. 



From the slipping lee cliff of a sand-dune at 

 Abu Racan, near Ismailia, I collected a sample of 

 sand by pushing in a wide-mouthed glass bottle. 

 The position was about the centre, under the peak, 

 of a rather long transverse dune about 40 feet 

 high. Here the air eddies vertically round and 

 round, winnowing the sand. The uniformity of the 

 material which remains is remarkable, Plate IX. 

 reproduced from a micro -photograph, illustrates 

 this, but the fact is more strikingly shown by 



