METEOROLOGY AND ALLIED SUBJECTS. 



277 



above the soil, and 29™ above the sea, and also the temperature of the 

 spring water : 



For the temperature of the earth we must refer to the original memoir 

 published by the Academy of Sciences, Montpellier, Vol. IX. In winter 

 and spring the plateaus of the Avennes, which rise to an altitude of 

 2,500 feet, are covered with snow, and the northwest mistral precipi- 

 tates itself with great force from these down upon the warm lowlands 

 to the southward. At this time the atmosphere at Montpellier is very 

 dry, and of wonderful clearness. This fators the radiation at night, and 

 the insolation by daytime thereby increasing the magnitude of the daily 

 variations of temperature. The mistral occurs most frequently in the 

 spring-time, and these beautiful days are known as the " cavalier." In 

 the summer-time the ijlateaus are greatly warmed up, and the mistral 

 loses its force and frequency. In the autumn the temperature is most 

 uniform, and the mistral least frequent. The intensity of the mistral has 

 a well-marked diurnal period; it increases as the sun approaches the 

 meridian in proportion as the sea-shore is warmed up. It ceases during 

 the night-time to begin again about 9 a. m. {Z. 0. G. M., Vol. XV, 

 1860, p. 455.) 



Mahlen has studied the observations of temperature of 118 years at 

 St., Petersburg, being nearly the whole of the interval 1743 to 1S7^'. 

 Among his results we find the following: The coldest day of the normal 

 year was January 24 ; temperature, — 9.7° ; the warmest day was July 

 23, 4-70.9°; the mean temperature of the year is -|-3.72o, which is the 

 same as the mean temperature of April 23 and October 21. The vari- 

 ability of the daily temperature is such that in winter 2,300 years, but 

 in August 380 years, of observation would be required to obtain daily 

 means, whose probable error is ± 0.1° 0. The mean departure of daily 

 means from the annual average is greatest for January 20 (0.23° C) ; the 

 least is for August 28 (2.13° C). The greatest absolute variation for 

 any one day is from +5.2° on January 4, 1771, to —37.4° January 4, 

 1814. The coldest January occurred in 1814, and the warmest in 1806. 

 The coldest July occurred in 1878, and the warmest in 1757. The c<Dldest 



