580 



SCIENCE. 



[N. S. Vol. II. No. 44. 



terized by such force and degree as to ren- 

 der them destructive to lives and property, 

 a forecaster of average ability and well- 

 balanced judgment is able to make nearlj' 

 or quite as accurate a forecast as when the 

 air pressure is quite uniformly distributed 

 and all changes of weather are so slight as 

 to be of no importance. 



If, then, a destructive frost or cold wave 

 can be predicted as easily as a change of a 

 few degrees in temperature, and if the 

 coming of high winds and gales are as easily 

 foretold as that of a gentle zephyr, it is 

 evident which class of forecasts should re- 

 ceive the greater attention. The public 

 care comparatively little for predictions of 

 moderate changes, and but little credit at- 

 taches to the Bureau when such forecasts 

 are verified, but when great heat, cold 

 waves or violent winds are on the pro- 

 gramme, a vital interest is felt in the sub- 

 ject, and the accurate forecasting of such 

 conditions is the gauge by which the public 

 measures the usefulness of the Bureau. 



Horticulturists and the growers of tobacco 

 and cranberries realize the vast benefit to 

 be derived from accurate frost predictions, 

 and I will give a brief statement of what I 

 believe to be original ideas introduced into 

 the making of frost forecasts while in charge 

 of the State Weather Service of Wisconsin, 

 a State including within its domain the 

 largest area of cranberry marshes in the 

 world, and also including an extensive area 

 devoted to the cultivation of tobacco. Here- 

 tofore I believe that only the air conditions 

 have been taken into consideration in the 

 making of frost forecasts — such as pressure, 

 temperature, relative humidity, cloudiness 

 and wind velocity. As a result of my in- 

 vestigations systematically prosecuted for 

 three years I found that the conditions of 

 the soil were equall}' as important as those 

 of the air. 



When the high-pressure area is moving 

 in from the west, clear and colder weather 



anticipated, with the probability that the 

 early morning temperature will permit the 

 formation of frost, the most important ele- 

 ments to be considered, in determining 

 whether or not frost will occur injurious to 

 growing crops, are as follows: 



First: Has rain recentlj' fallen, and what 

 is the condition of the soil relative to the 

 amount of moisture contained ? 



Second: What are the natural properties 

 of the soil relative to the slow or rapid loss 

 of heat by radiation ? 



Third: To what degree of heat has vege- 

 tation been subjected during the period im- 

 mediately preceding? 



The early fall frost injurious to tender 

 crops occurs with the observed town or 

 telegraphic minimum temperature rang- 

 ing from 40 to 50 degrees, because, when 

 the early morning temperature in the town 

 falls much lower than 40 degrees, it is usu- 

 ally so late in the season that all crops are 

 gathered, or if not gathered thej^ have been 

 destroyed ere this condition arrives. At 

 the time then that frost warnings are of 

 most benefit we have to deal with the air 

 at temperatures considerably above the 

 freezing point, and to recall that a depo- 

 sition of frost requires that the tempera- 

 ture of the top soil, or that of vegetation, 

 be reduced to the freezing point. This, of 

 course, is accomplished by conduction and 

 radiation of heat which takes place more 

 rapidlj' from the soil and vegetation than 

 it does from the lower stratum of air to the 

 higher. 



Anything that will seriously interfere with 

 a rapid loss of heat after nightfall will tend 

 to prevent the formation of frost. Moisture 

 does this, and if the soil be well charged it 

 partakes greatlj' of the stabilty of water 

 as to temperature, and cools but little, if 

 any, below the temperature of the superin- 

 cumbent air, and no frost will occur even 

 though all other favorable conditions of 

 clearness, gentle winds and cool air obtain. 



