Frost resulting from cooling of vegetation by nocturnal radiation is a serious agricultural problem. Because of the number of variables involved, attacks on this problem from a purely theoretical point of view have met with only moderate success. It seems logical to suppose that an instrument might be devised which would speed up the natural radiation processes and enable an observer to obtain in a few hours a measure of the cooling which occurs naturally over a period of 12 to 14 hr. Such an instrument could serve as a frost warning device. This paper describes the construction of a radiation device and presents experimental evidence to show that it can be used as a predictor of freezing temperatures at vegetation level.