1918.1 METEOROLOGY. Yl? 



found, wo can always determine its natural sine. Thus, in the examples now 

 quoted, the .sines of 16° .42' and 77° .28' are known, respectively, to be 0.287 

 and 0.976. The final measure of the influence of the rainfall of 0.3 in. is 0.287 

 and of 4.5 in. is 0.976. A reference to the diagram (fig. 1) will show how 

 rapidly the measure increases with the rainfall at first, but that after the rain- 

 fall has reached what we assume to be near the optimum amount the measure 

 becomes practically constant." 



The figures for temperature and rainfall are combined by means of a triangle, 

 one side of which has units of length equal in number to the number of suffi- 

 ciently warm days and the other units of length corresponding to the number 

 of sufficiently warm nights. " If the angle between these two sides be the angle 

 whose tangent is the rainfall, then the area of the triangle is equal to the prod- 

 uct of those two sides into half the sine of the included angle. Or more briefly, 



Index-area=FdXF»iXi sine arc tan R 



where Fd is the frequency of warm days, and F» the frequency of suflaciently 

 warm nights, and R is the total rainfall for the month. Now, since the fre- 

 quencies and the rainfall are 

 variable for the months and 

 for the stations, we shall ob- 

 tain a .series of areas which 

 may be entered on a map and 

 differentiated by lines in the 

 usual manner." Charts illus- 

 trating the application of the 

 method are given. 



Where wheat is grown 

 ( U. S. Dept. Agr., Nat. Weather 



and Crop But., No. 7 (1918), ~ / ~2 3 ^ 5 & ^ 



pp. 2, 3, figs. 5).— Two charts a>^^a/^^^^ r/AVCH£SJ 



.,,,,. ^, J. ^ ., ^. -. Fig. 1. — Efficiency of varying amounts of rainfalL 



illustrating the distribution of 



winter wheat growing in the United States and one chart showing the world 

 wheat acreage are given and discussed. It is stated that " the ideal climate for 

 wheat is one v/ith a long and rather wet winter, prolonged into a cool and rather 

 wet spring, which gradually fades into a warmer summer, the weather growing 

 gradually drier as it grows warmer, with only comparatively light rains after 

 the blossoming of the crop, just enough to bring the grain to maturity, with 

 abundant sunshine and rather dry air toward the harvest, but without dry 

 and scorching winds until the grain is fully ripe ; and then hot, dry, rainless 

 weather until the harvest is gathered." 



Spring frosts {TJ. 8. Dept. Agr., Nat. Weather and Crop Bui., No. 4 (1918), 

 pp. 2, 3, 7, S, figs. 3). — Three charts are given and explained showing (1) dates 

 of planting in seven zones into which the eastern part of the United States has 

 been divided, (2) dates in spring when killing frost occurs on the average only 

 1 year in 10. and (3) average dates of last killing frost in spring. 



Storm rainfall of eastern United States, A. E. Moegan and C. H. Paul 

 (Miami [Ohio'\ Conserv. Dist., Tech. Rpts., pt. 5 {1917), pp. 310, pis. 3, figs. 

 111). — This report gives in detail the results of an extended study of storm 

 rainfall and run off in the United States east of the 103d meridian. 



This study was undertaken in connection with an engineering examination of 

 the Miami Valley, begun immediately after the subsidence of the great flood 

 of March, 1913, for the purpose of determining the best plan for preventing 

 damage by future floods. Every record of storms of consequence within the 



