METEOROLOGY. 523 



tober the minimum, 34.4 hours, or 10 per cent, of the possible total. The 

 mean cloudiness for three observations daily, at 7 a. m., 2 p. m., and 

 9 P. M., gives figures closely following the reciprocals of the percentages 

 of sunshine. (Z. 0. G. 31., xvn, p. 100.) 



Prof. J. Liznar has investigated the relation between the eleven-year 

 sun-spot period and the daily and annual variations of terrestrial tem- 

 perature. For the daily variation he studies observations at thirteen 

 stations, and finds that a maximum of sun-spots corresponds to a min- 

 imum of daily variations, but the latter occurs about two years earlier 

 than the former, a result agreeing with the similar variation in mean 

 annual temperatures discovered by Koppen. Liznar has also studied 

 the annual temperature variations, by means of three long series of ob- 

 servations extending from 1699 to 1873; he finds a close agreement 

 between these and the maxima and minima of sun-spots from 1098 to 

 1750; but for the succeeding 00 years, like all previous similar investi- 

 gations, these relations are disturbed and even completely inverted, the 

 maxima of sun-spots now corresponding to minima in place of maxima 

 of temperature. The relation between sun-spots and temperature is 

 therefore still entirely unknown. (Z. O. G. M., xvn, p. 495.) 



G. von Boguslawski gives a summary of Hanu's memoir on the tem- 

 perature of the southern hemisphere. The latter has carefully combined 

 a number of recent observations, and has deduced a general formula 

 fo. the temperature of southern latitudes apparently somewhat more 

 reliable than those of Dove (1852), Hopkins (1852), Forbes (1859), Sar- 

 torius von Waltershausen (1865), and Ferrel (1871). He arrives at the 

 f 1 lowing formula for the mean aunual temperature at any degree of 

 southern latitude: 



T<p = 26.0° + 6.94<fcsin? — 45.28° sinV 



According to this formula the southern hemisphere is warmer than 

 the northern for all latitudes higher than 45°, the differeuce amounting 

 to 1£° at parallel 60 S. latitude. Forbes had arrived at exactly the 

 same result, namely, 42£°. (Z. O. G. M., xvn, p. 410.) 



Bilwiller notes that the severest cold weather in Switzerland always 

 occurs when snow covers the ground; and that all hough the descending 

 currents of air in anticyclones are visibly warming the air, yet at the 

 ground severe cold is observed. "The influence of the snow on the 

 temperature of the lower air lies in the fact that as a poor conductor of 

 heat it breaks the connection between the earth and the air. The tem- 

 perature changes at slight depths below the earth are f r smaller and 

 slower than on the surface. In December the earth is decrle<lly warmer 

 than the air which is thus warmed from below. If snow lies on the 

 ground it cuts oil' this supply of heat from the air. The surface of the 

 snow cools very rapidly by radiation under a clear sky, and this loss of 

 heat is communicated directly to the air, but only very slowly to the 

 earth. If the snow covering is wanting, an exchauge of heat occurs 

 between air and earth, preventing such a very low temperature in the 

 lower-air stratum." (Z. O. G. M., xvn, p. 98.) 



