52 The Principles of Fruit-growing. 



perfectly still. This is well illustrated in the vagaries 

 of light frosts, which touch here and there where the 

 air is the stillest or the radiation most rapid. This 

 is particularly true in the growing months, when the 

 earth becomes very warm during the day and loses 

 the heat rapidly at nightfall, and when, also, the 

 sky is less overcast by clouds than it is in the win- 

 ter months. After studying the disastrous frosts of 

 May, 1895, in the Chautauqua vineyard district, 

 Tarr wrote* as follows : " The behavior of this frost 

 was altogether remarkable, leaving some districts or 

 vineyards almost unharmed, and nearly ruining the 

 crop in others, while even in the same vineyard these 

 extremes were sometimes noticed. This was probably 

 chiefly due to eddies of the air, for even though air 

 is almost quiet, it is still in uneven motion. One 

 may see this illustrated on a calm day by noticing 

 the movements of a column of smoke. The air, be- 

 ing invisible, does not reveal these movements, and 

 we become aware of them only when the conditions 

 are exceptional, as when a frost is dealing out de- 

 struction to vegetation. The condition of the ground 

 also affects the frost, and the question whether it is 

 dry or moist, freshly plowed or turf covered, whether 

 there are trees or pastures or plowed ground in the 

 neighborhood, all have their influence ; but this sub- 

 ject has never been properly studied, and it is not 

 possible to state just how these differences affect 

 frost action." 



Much of this unrecognizable movement of the air 



*Bull. 109, Cornell Exp. Sta.. 121. 



