334 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
PRESERVATION OF CROPS FROM INJURY BY FROST. 
By Alexander McAdie, 
Professor of Meteorology at Harvard University, formerly in charge 
of the Weather Service of the United States for California. 
Throughout Christendom at the present moment the uppermost topic 
of discussion is food. The outcome of the war for Liberty, as we believe 
it to be, will depend largely upon the supply of food. In the countries 
of the Allies as well as in Central Europe every effort is being made to 
increase the crop yields. This is done by increasing the acreage and 
by intensive cultivation. Fertilizers are used as never before, and 
where formerly a few tons of manure were regarded as sufficient for 
an acre of ground, to-day in places one hundred tons are employed. 
Farming operations are carried on during the night as well as the day, 
labourers go to their work in shifts so that no time may be lost, tractors 
do the work of many horses, and in every direction there is striving for 
a maximum yield. Those of us who are not farming or gardening do our 
bit by lessening the demand, practising economy, and preventing waste. 
In this last-named effort, namely, the prevention of waste, it would 
seem wise at this time to study natural wastage, for Nature itself is the 
master spendthrift ; and the loss by natural conditions, such as pests, 
drought, and frost, may easily exceed the savings of the community 
for a long period. Now is the time, if ever, when united and properly 
directed effort should be made to reduce the loss occurring through 
frost. In this paper we shall not stop to consider spring frosts and 
the losses due to tender vegetation, reserving this discussion for a later 
paper, but shall consider only the autumnal frosts, when vegetation is 
advanced and nearly ready for the harvest ; and when loss therefore 
is doubly disastrous. 
We shall consider the theory and practice of frost-fighting, first from 
the aerographer's standpoint, and later from the grower's point of view. 
I. 
Frost, in the general acceptance of the term, means a temperature 
of freezing or below, and of sufficient duration to result in damage to 
the cell tissues of plants near the ground. The loss of heat from both 
ground and plant is chiefly caused by radiation. The control is the 
now of air plus water vapour near the ground. In other words, frost 
is to be regarded as a problem in local air drainage. The duty of the 
forecaster is to detect and give warning when conditions favour local 
stagnation and intense radiation. Can this be done successfully ? 
Yes. For these conditions may be expected when an area of low 
pressure or surface depression moving rapidly eastward is followed by 
