934 



SCIENCE 



[N. S. Vol. XLIII. No. 1122 



bination of heat and smoke ; in the best orchard 

 practise there is a fairly clean-burning small 

 fire to each one or two trees. Economical and 

 effective use of heaters involves the informa- 

 tion and warnings issued by the U. S. Weather 

 Bureau, and knowledge of the local seasons of 

 frost and places of lowest temperature. The 

 methods of protection should be studied, and 

 the type which has proved successful in the 

 particular region or in one where the condi- 

 tions are similar should be selected. The cam- 

 paign should be carefully planned in advance. 

 Protection is so expensive that crops of high 

 value only can carry the charge. 



Protection is but one aspect of the frost 

 problem. The problem for the farmer is' to 

 determine the frost conditions he will have to 

 meet and to arrange his crops and his agricul- 

 tural practise to suit these conditions. Appar- 

 ently, the first frost maps of the United States 

 were made by Mr. P. C. Day.^ Maps are pre- 

 sented showing average and extreme dates of 

 the last killing frost in spring, and of the first 

 in autumn, and the average length of the grow- 

 ing season. Isochronal lines are shown east of 

 the Rocky Mountains, and figures are given at 

 stations west of the mountains. Later, more 

 extensive frost data, included in the original 

 records of the cooperative observers of the 

 Weather Bureau, were edited, and tabulated; 

 and new frost maps of the United States have 

 been constructed on a scale of 1/2,500,000, the 

 records used being within the period 1895 to 

 1914. In this work the Office of Farm Man- 

 agement and the Weather Bureau cooperated. 

 A preliminary study of these maps was pre- 

 sented by Mr. Eeed at the Second Pan-Ameri- 

 can Scientific Congress. Parts of the author's 

 abstract are quoted here : 



Trill ing frost ... is a temperature low enough 

 to destroy plant tissue. Frost is measured by the 

 effect on plants, but it would be better to use some 

 definite temperature. 



Most of the United States is subject to annual 

 killing frosts. Low temperatures are most dan- 

 gerous to plants at the beginning and end of the 

 growing season. Frost is an anticyclonic phe- 



3 Weather Bureau Bulletin V., 1911, 5 pp., 5 

 maps. 



nomenon. East of the Rocky Mountains it is fre- 

 quently possible to follow a frost across the coun- 

 try ; west of the Kocky Mountains frost occurs when 

 an anticyclone overlies the region. 



Records of frost occurrence are now available 

 for over 5,000 places. These may be supplemented 

 by knowledge of topography and vegetation, and 

 although the term is of doubtful meaning, ' ' aver- 

 age dates ' ' of killing frost may be determined. 

 Frost risks may be determined by the use of the 

 ' ' standard deviation. ' ' Maps of the average date 

 of last killing frost in spring, and the frost kill- 

 ing in autumn, and of the length of the season 

 without killing frost have been drawn. Between 

 one quarter and one third of the country is sub- 

 ject to frost after June 1 and before September 

 1. Computed dates of last spring frost and first 

 autumn frosts in nine years in ten, as well as the 

 length of the season without killing frosts in four 

 years in five, have been mapped. 



Mouutaia masses are more subject to frost than 

 lower regions, but the relations are complicated 

 by "air drainage," which makes frost more com- 

 mon in valleys than on slopes. . . . 



Mr. Heed and Miss Cora L. Feldkamp have 

 published a " Selected Bibliography of Frost 

 in the United States." * It is arranged with 

 the later papers first, as most of the work is 

 very recent; earlier papers cover substantially 

 the same ground. Thus 26 of the 94 articles 

 are dated 1914 or 1915. An index by states is 

 added. Although the titles are few in num- 

 ber, they were selected from all the material 

 on " frost and frost prevention under Ameri- 

 can conditions," found in the libraries of 

 Washington, the published bibliographies of 

 the John Crear Library (Chicago), and refer- 

 ences in many agricultural and meteorological 

 magazines and other publications. 



WEATHER AND THE WAR 



There are two aspects of the relationships 

 between weather and the war: weather has a 

 decided control on military operations; but it 

 is a question whether the war has any effect on 

 the weather. Professor R. DeC. Ward has 

 undertaken a thorough study of the former, 

 and has published some of the results in the 



4 Monthly Weather Eeview, October, 1915, pp. 

 512 to 517. 



