EFFECT OF WOODLANDS UPON DEWS: DRIFTING SNOWS 281 

 Citing from I. T. Thomas, he continues : 



Another important advantage has been occasionally afforded by the shelter of wood- 

 lands. It is well known that rust in wheat is commonly most prevalent on low and 

 mucky lands, yet at other times, and in its most virulent form, it seems borne on the 

 wind, and often destroys thousands of acres on all kinds of soil in one sweeping blight. 

 An instance of this kind occurred in Northern Indiana in 1840. Early and late sown, 

 on compact and spongy soil, on hill and dale, cleared land and prairie, were all alike 

 affected. In every instance, however, where the crop was sheltered by woodland it 

 was least injured. An extensive farmer in Ontario County, New York, informed me, 

 some years ago, that out of two hundred acres of promising wheat, which be then had 

 growing, all was completely destroyed except those portions slieltvted hy woods, the total 

 loss being four or tive thousand dollars, most of which he believes would have been 

 saved had his land been protected by timber belts.i 



Frost and dews, as affected by timher belts. 



The protection of winter grain from winter-killing by proximity to 

 woodlands has often been noticed, and as an obvious inference, the pre- 

 vention of this injury by the planting of timber belts has been sug- 

 gested. 



The radiation and cooling of certain soils in summer nights is well 

 known to depend upon the absence of clouds or other covering to iu- 

 tercept and prevent it, and from this cause there may be no dew under 

 the shade, or within the influence of an isolated tree. It is during still 

 nights, when this process is most active, that summer frosts generally 

 happen. But on the other hand, the dew is more commonly abundant 

 near the border of a woodland, where the radiation may be less, yet the 

 moisture is more, and a less amount of cooling may be sufficient for 

 the precipitation of dew. 



It has also been noticed that a windy night is seldom a dewy one, and 

 it is quite probable that the greater amount of dew along the borders of a 

 grove may be in part occasioned by the calm in the air. " When the 

 dew is formed," says Kaemitz,* " it often disappears very quickly, if 

 the wind rises, or the atmosphere is disturbed," a circumstance most 

 likely to occur in the open fields. Under like conditions of moisture, 

 the greater amount of dew there is the greater is the cooling and the 

 tendeiicy to fro&t ; and instances may occur in which places within the 

 calm on the lee side of a woodland might freeze, while the open country 

 exposed to a gentle wind might escape. 



Shelter-belts for preventing liigliways against the obstruction of drifting 

 snows. Project of a laic. 



The importance of this subject is often realized in the Northern States, 

 where snows even of moderate depth, in places peculiarly exposed to 

 heavy winds, will often cause serious obstruction by drifting across the 

 roady.^ Various devices have been employed to prevent these evils, 

 such as high and close board fences, the removal of all fences in winter, 

 or wliat is nearly equivalent, the use of wire instead of rails or boards ; 

 but none of these appear so effectual as a close and well-kept screen of 



' Third Report of Trustees of Illinois Industrial University, p. 361. 



* Meteorology ; Walker's Translation, p. 107. 



3 Travellers on the Union Pacific and other railroads crossing the Plains, must hav9 

 noticed the devices suggested by experience for arresting these drifts. The snows 

 migh"-, not fall more than a few inches deep, but would accumulate in places to many 

 feet in depth. Besides snow-sheds entirely covering the road in places of great ex- 

 posure, board fences across the direction of prevailing winds, and sometimes 5 or 6 of 

 these in succession, have been placed, with the view of precipitating the snows before 

 reaching the track. Some of these are movable, and are raised two or three times dur- 

 ing the winter, as they become buried. In places where the planting of broad ever- 

 green belts is possible,"^ they would doubtless prove an effectual remedy. 



