TRANSACTIONS OP SECTION E. 817 



to rld^e, -which were rapidly iucreasin<r in size. The steep side faced the wind. 

 The ridges, which were pretty accurately parallel one to another, were transverse 

 to the wind, but with much sinuosity, no ridge being straight for more than a few 

 inches. It is evident that the wind must be concentrated in the re-entrant angles 

 of the steep weather slope, and this would tend by rapid erosion to destroy the 

 arrangement of long transverse lines which is the most obvious characteristic of 

 ripples. The ridges, however, did not lose their transversality, which was 

 apparently preserved by the greater deposit of drifting snow in these re-entrants, 

 which stopped the threatened gaps; and by the collapse of the overhangmg 

 cornice of uncompacted snow at the salient angles, bv which these promontories 

 were truncated. 



Case III. — The latest-fallen layers of snow having been blown away, the wind 

 acts upon compacted snow (this was generally in drifts which had become exposed 

 owing to change of direction of wind). The wind abraded a fine granular ' drift,' 

 which did not adhere to the smooth hard surfaces. Parallel lines of bevelling or 

 grooving transverse to the wind are the most conspicuous feature of the resulting 

 structure in the compact, almost homogeneous, fine-grained material. The 

 lines are much freer from minor irregularities than the ripples described above. 

 As the action continues, however, the sinuosities are emphasised, for, the ' drift' 

 not adhering well, the re-entrants are cut back more and more behind the 

 salients. Further, the wind concentrating along the lines of the re-entrants, the 

 general level of the surface here is lowered more quickly by abrasion than is the 

 case along the intermediate lines of the salient angles. Thus is produced a well- 

 marked form transitional between snow ripples and sastrugi, in which inter- 

 mediate form the transverse ridges are crossed at right angles by alternate rido-es 

 and furrows parallel to the wind, the furrows being along the line of the re-entrants. 



Sastrugi. — This action went on until the ridges transverse to the wind were 

 merely a subordinate and scarcely noticeable feature, and the snow was seen to be 

 in great ridges parallel to the wind. These corresponded perfectly with the 

 sastrugi of the Tundras as described by A. Penck ' on the authority of F. Schmidt 

 and G. Bore. 



On the opposite orientation of snow ripples and sand n>;>/^s.— Eipples in loose 

 sand have their steep faces on the leeward, snow ripples on the windward side. 

 The exposed face of the snow ripple becomes steeper than the sheltered face* 

 because the cohesiveness of the snow while in mass enables the wind to carve out 

 wind caves, in which its force is concentrated. In loose sand the slipping of the 

 material prevents this. The friability of the snow also assists in the effect, the 

 detailed explanation of which would, however, be too long for this abstract. 



Observations were also made upon the forms of snowdrifts. 



Photographs were taken of ripples, sastrugi, and drifts. 



4. The Geographical Distribution of Relative Humidity. 

 ByYi.G. Ravenstein. 



The author stated that the importance of relative humidify as a climatic factor 

 was fully recognised. Having illustrated its influence upon organic life, upon 

 agriculture and human industries, he expressed his regret that neither in number nor 

 in trustworthiness did humidity observations meet the requirements of a person 

 desirous of illustrating its distribution over the globe by means of a map. This was 

 owing largely to defects in the instruments employed, incompetence of the observers 

 and unsuitabUity of the hours chosen for the observations. As to the humidity over 

 the ocean, we were still dependent upon the observations made onboard passing 

 vessels, and he was afraid that the time had not yet come when floatincr meteoro- 

 logical observatories would be stationed permanently throughout a whole year at 

 a few well-chosen localities in mid-ocean. Notwithstanding this paucitv of 

 available material he had ventured, in 1894, to publish in Philip's ' Systematic 

 Atlas a small chart of the world showing the distribution of humidity. The 



' Morph. der Erdolerfldcke, vol. i. pp. 388, 889. 

 1900. 3 ^ 



