Predicting Frost 255 



and light wind, is considered critical; particularly is this the case if 

 the rate of fall approximates 1° for each two hours, which, if con- 

 tinuous — as would be Mkely with a clear sky and light wind — ^would 

 bring the temperature close to the freezing-point by early morning. 

 A fall in temperature of 2° an hour would indicate frost, even with 

 the temperature considerably above 40° in the late afternoon. 



' Atmospheric pressure. — ^The rate of change in the pressure of 

 the atmosphere, as indicated by the barometer, is of some assistance 

 in forecasting frost. The actual stage of the pressure, whether above 

 or below normal, is not important, except that a warm period with 

 unusually low pressure is likely to be followed by the opposite 

 extreme. The important factor is the rate of change. If the pressure 

 is increasing rapidly, as indicated by a rapid rise in the barometer, 

 it is a good indication that the cold period or cold wave is approach- 

 ing rapidly. The change in pressure usually precedes by a short 

 interval the change in direction of the wind, because the wind 

 depends on the pressure; but one will have to watch the barometer 

 very closely to gain much advantage over the indications afforded 

 by the direction and force of the wind." 



Mulching to enable plants to escape frost. 



It is a general opinion that a mulch or heavy cover 

 placed about plants on the earth when it is frozen, will 

 retard flowering and the maturing of fruit; yet the practice 

 appears to be often unsatisfactory, and there are reasons 

 for supposing that the philosophy of the subject is not 

 commonly understood. The subject is one of increasing 

 importance, for it is essential that every means be used to 

 escape late spring frosts. Efforts must also be made to 

 reach the market when there is least competition from 

 other sources, and, in the North, at least, this competition 

 comes chiefly from early products produced in states to 

 the southward. 



If the plants are such that they can be entirely covered 

 (as the strawberry), mulching will retard them; but the 

 mulching of the earth does not greatly affect the blossom- 



