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, 
