514 EXPEEIMENT STATION EECORD. 



servations by Church at Reno and on Mount Hose (E. S. R., IS, p. 520) are 

 also referred to as confiriuing this conclusion. 



Indications of approaching' frost, R. Strachan (Quart. Jour. Roy. 2Iet. Soc. 

 [London'l, SJ/ (I DOS). Xo. i'/J, pp. //7-.70). — Data are adduced to show that "in 

 the majority of cases the evening dewpoint is no indication of frost unless the 

 sky during the night becomes clear, or a radiation fog is on the ground with a 

 clear sky above it. . . . For the purpose of making forecasts the psychrom- 

 eter should be noted at or after sunset, or at 9 p. m., and the amount of cloud 

 at the time, and during the fore part of the night if convenient. The dew-point 

 can then be found by Glaisher's Hygrometrical Tables, or roughly by taking 

 the difference between the two thermometers from the reading of the wet-bulb. 

 "When the dew-point is at or below 32°, frost is in evidence, but may be evanes- 

 cent, due to a rise of temperature, with change of wind, rain, or overcast sky. 

 Even when it is above 32°, if the sky is clear it is probable that the tempex-a- 

 tui'e on the ground will go low enough for frost to form." 



A two years' study of spring' frosts at Williamstown, Mass., W. I. Miliiam 

 (Mo. Weather Rev., 36 (1908), Xo. 8, pp. 250-254, flff- i).— This article gives 

 reference to recent articles on frost prediction and protection, and summarizes 

 the results of observations at 10 frost stations located in different parts of 

 Williamstown. The following conclusions, which apply not only to Williams- 

 town but probably to the whole of New England, are drawn from the results : 



" The so-called spring frosts may be expected from the last of April until 

 the first of June and occur on still, clear nights, with the wind almost invari- 

 ably from the northwest. They are likely to come on the first or second night 

 following the passage of a low and the transition of the weather control to an 

 area of high pressure. This facilitates both the importation of colder air and 

 radiation, the two processes which cause the low temperatures required. The 

 air is so dry and the dew-point lies so low that it plays no part whatever in 

 determining the amount of the drop from the maximum to the following 

 minimum. The drop is, however, far from a constant, and must be estimated 

 for each individual case, taking into account the probable characteristics of the 

 afternoon and night. 



" If, after the probable minimum temperature in the thermometer shelter 

 has been estimated, it is desired to detei'mine what the probable temperature 

 of low-gi'owing vegetatioH in the coldest part of the limited area will be, three 

 things must be taken into account. First, that plant temperatures go below the 

 real air temperatures, because the plants are in the open without such a hin- 

 drance to radiation as is the shelter about a thermometer : second, that vegetation 

 is located near the ground and not at the height of the instruments in the shel- 

 ter ; third, that the variation in temperature over a limited area may amount to 

 several degrees. Were this computation carried out with the average values 

 for Williamstown, about 2° would be allowed for exposure in the open, 3° for 

 height, and 6° for variation between the shelter and the coldest part of the 

 area. Thus the temperature of vegetation in the open, near the ground, in 

 the coldest part of the village may be expected to average 11° lower than the 

 estimated mininunn in the shelter as it is now located." 



Monthly Weather Review (Mo. Weather Rev., 36 (1908), Nos. 7, pp. 197-230, 

 figs. 10, charts 6; 8, pp. 231-27 Jf, figs. Jf, charts 9). — In addition to the usual 

 reports on forecasts, warnings, weather and crop conditions, meteorological 

 tables and charts for the months of July and August, 1908, recent papers bear- 

 ing on meteorology, recent additions to the Weather Bureau library, etc., these 

 numbers contain the following articles and notes : 



No. 7. — Rain-making in New Zealand ; Report upon the Dry Period and Rain- 

 making Experiments at Oamaru, New Zealand (illus.), by D. C. Bates; Inter- 



