RESULTS OF MEASUREMENTS. 43 



DRIFTING OF SNOW. 



A shelter belt may be so placed as to act as a "snow trap/' since 

 the snow will be dropped in the lee of the windbreak, where the 

 force of the wind is slight. On this account objection is often made 

 to windbreaks which stand on the north or west side of roads and 

 which cause a large amount of snow to be deposited in the road. 

 This may to some extent be prevented by placing the windbreaks 

 on the side of the road opposite to that from which the prevailing 

 winds come, or, better still, by making the windbreak on the wind- 

 ward side of the road wide enough to completely check the wind 

 and to collect the greater mass of snow under the trees. 



Kailroads are particularly interested in windbreaks for snow pro- 

 tection, since even a light fall of snow, if blown into a railroad cut, 

 may stop traffic. To protect their tracks from snow, railroads have, 

 in mountainous regions, constructed many miles of snow sheds, and 

 in the Plains region have placed artificial windbreaks in the form of 

 board fences, often in series, at some distance from the track, on the 

 windward side. A few desultory attempts have also been made to 

 protect railroad cuts with bodies of timber, but in most cases the 

 wrong species were selected, little care was given the trees, and the 

 windbreaks are a practical failure. Yet this scheme of protection, if 

 properly carried out, would not only save the railroad companies large 

 outlays for the construction and maintenance of their fences, but 

 would utilize the land within their rights of way for the production of 

 posts and ties, and prove of esthetic value as well. The practical 

 objection to this would be the necessity for acquiring wider rights of 

 way on the windward sides of the cuts. 



V. EVAPORATION. 



Except when it is completely saturated, the air 1 is constantly taking 

 up moisture from the surface of ponds, from the soil, from the foliage 

 of vegetation, and even from bodies of snow and ice, and this evapora- 

 tion is always enhanced by any movement which has the effect of 

 distributing the aqueous vapor as it is formed, and thereby pre- 

 venting local saturation. The change to the vaporous state requires 

 a great deal of heat. This heat is in part supplied by the air and 

 partly by the object which is losing its moisture. 



1 The term "air" is used in the popular sense throughout this and other discussions. It is well under- 

 stood that the formation of aqueous vapor is independent of the air, and that this gas is only mixed with 

 the gases of the air not a part of it. The temperature and dissemination of aqueous vapor are so entirely 

 dependent upon the temperature and movement of the air, however, that the two terms become insepa- 

 rable in common usage. 



