1919 J METEOROLOGY. 119 



The normal daily march of temperature is closely allied with the amiual 

 march in establishing the vegetative period. In most of the country the average 

 frost-free date in spring corresponds to a mean daily temperature of from 52 

 to 66°, except along the central and north Pacific coast, the region of the Great 

 Lakes, and along the middle and north Atlantic seaboard, >vhere the tempera- 

 tures are lower. Similar data for fall frosts are in close agreement with those 

 for spring fi'osts. In limited areas, however, the first fall frost occurs on the 

 average while the mean daily temperature is a degree or two higher tlian is 

 necessary to cause a cessation in spring frosts in an average year. "Consid- 

 ering the records for all stations throughout the country the mean daily tem- 

 perature on the average date of the last killing frost in spring is 52.1°, and 

 on the average date of the first in fall it is 52.6°. . . . Owing to the fact that 

 these temperatures corresponding to the average frost dates are so uniform, 

 it is possible to determine very closely the average frost dates from the mean 

 daily temperatures. . . . 



"The only locality .in which the frostless season is longer than the vegetative 

 period is comprised in a small area along the north Pacific coast. In most 

 of Washington, portions of upper Michigan and much of Minnesota, as well 

 as along the north Atlantic seaboard, killing frost shortens the vegetative period 

 by less than 20 days, but in much of the central portion of the country the 

 difference in the two periods ranges from 40 to 60 days. From Virginia, Ken- 

 tucky, Missouri, and Oklahoma southward this difference increases rapidly 

 from 60 to more than 100 days in the northern portions of the Gulf States. 

 Southward from the upper Mississippi Valley to southern Arkansas the differ- 

 ence increases from 20 to 100 days, or from less than one to more than three 

 months." 



Increase of precipitation with altitude, A. J. Henry {U. S. Mo. Weather 

 Rev., lil (1919), No. 1, pp. 33-41, figs. 2). — Reviewing observations bearing upon 

 this subject in different parts of the world, the author concludes that " the 

 main features of the precipitation-altitude relation are essentially as follows : 



" The trend of the mountains must be in such a direction as to cause an 

 ascent of the air masses which encounter them. Mountain systems whose axes 

 are parallel, or nearly so, with the direction of the rain winds cause little or 

 no increase in precipitation. 



" The inclination of the slope of the mountain is of great Importance ; the 

 steeper the slope, other things being equal, the greater the precipitation. The 

 quantity of rain or snow which falls anywhere is also conditioned upon the 

 initial temperature and relative humidity of the air at the beginning of the 

 ascent. Obviously, it also depends, in no small degree, upon the duration of 

 the winds from the rain quarter, or, in other words, upon the rate of move- 

 ments of the atmospheric disturbance with which the rain winds are 

 associated. 



" The altitude of the zone of maxinmm precipitation appears to vary slightly 

 with latitude, being lowest in the Tropics — a little less than 1,000 meters — and 

 highest in temperate latitudes, say, between 1,400 meters and 1,500 meters. It 

 has also a seasonal variation, being highest in summer and lowest in winter." 



The rainfall of Erance: Variations with altitude, E. Mathias {Compt. Rend. 

 Acad. Sci. [Paris], 168 (1919), Nos. 2, pp. 105-108; 4, pp. 239-21,2; 1, pp. 358- 

 360, fig. 1; abs. in Rev. Sci. [Paris], 57 (1919), No. 2, pp. 61, 62 ;i U. S. Mo. 

 Weather Rev., 47 (1919), No. 1, p. 41)- — The author concludes from observations 

 at different places and altitudes that " the precipitation-altitude relation in 

 France may be expressed closely with the formula, R=Ri+fcA — fc'A^ in which 

 R represents the rainfall in millimeters at altitude A (in meters), Ri the i-ain- 

 fall at a lowland station, k the coefficient of increase with altitude, and k' A' a 



