A penny saved is twice earned said Franklin, and one can not help wondering what that wise old gentleman would say today about food conservation and especially the problem of saving crops from injury by frost. Throughout Christendom at the present moment the uppermost topic of discussion is food. Apparently the outcome of this great war will be largely determined by the supply of food. In our own land as well as in other lands every effort has been made to increase the crop yield by adding to the acreage and by intensive cultivation. Fertilizers have been used as never before, farming operations go on by night as well as by day, tractors do the work of many horses, and in every direction there is intense striving for big harvests. Those of us who are not in the field do our 'bit by lessening the demand, practicing economy, and preventing waste. Is it not wise, then, to study natural wastage in all its forms ? For Nature herself is the master spendthrift; and the yearly losses through natural conditions, such as droughts, pests, and frosts, easily exceed the savings of the community for a long period. Now, if ever, is the time when every effort must be made to reduce the losses by frost. The problem is one in the geography of the lower air, or, in other words, is largely a matter of local air drainage. Frost can be mastered and, indeed, has been mastered in some localities. The word frost has been used in three different senses: first, a freezing temperature; second, the spicular ice crystals; and third, the damage resulting from defrosting or frosting. The first is an erroneous usage and should be abandoned. The second interests the aerographer, or student of air motion and physics, while the third, which is the proper usage, interests the plant physiologist and the public. When water vapor in the air near the ground changes its form directly into ice we get the familiar spicular or pointed crystal which most of us call frost. It does not go through the intermediate state of being water, else would be frozen dew, and all the flakes would be little globes. After a still, clear cold night, with neither too much nor yet too little moisture present, we find next morning crystals covering the grass and lower foliage, and most of us think, if the deposit is at all heavy, that much damage has been done. If later the plants shrivel and blacken we think that the crystals did the mischief. On the contrary, Nature, through the agency of these crystals, was trying to cause a delay or lag in the cooling. By this very same method, which we shall later explain, namely the utilization of the fact that ice has a high specific