METEOEOLOGY AND ALLIED SUBJECTS. 323 



Soret has attempted an explauation of a fact frequently observed, 

 that the diffuse daylight is polarized even in those strata of air that 

 are in the shade. In the valleys of the Alps many opportunities occur 

 for observing this, and the maximum polarization occurs when the line 

 of sight is at right angles to the direction of the sun's rays. Soret's 

 exi)lanatiou is about as follows: 



The masses of air that lie in the shade are illuminated by the difluse 

 light of the upper strata upon which the sun's rays shine directly. It 

 can now be proven that the sum of the vibrations reaching a given 

 point fi-om the various portions of the celestial hemisphere must pro- 

 duce effects equal to those produced by one ray reaching this point 

 directly from the sun, and a second ray at right angles to the first and 

 polarized in a plane perpendicular to the direction of the. first. The 

 effect of the direct sunlight differs, therefore, from the sum of the effects 

 of the diffuse light only in this, that in the latter case the polarization 

 is not so complete. {Z. 0. G. M., 1879, XIV, p. 106.) 



Montigny has discussed the question of the twinkling of the stars as 

 measured by the number of the changes of color in a given interval of 

 time. The observations made by him during six hundred evenings 

 show that the dependence upon the rainfall is most prominent; but the 

 influence of other meteorological conditions is well defined ; thus, when 

 the temperature rises the twinkling diminishes in intensity, and the colors 

 lose much of their clearness, especially in summer. In the winter, 

 however, in the cold, dry weather, the twinkling is stronger and the 

 colors more brilliant. The presence of moisture, &c., appears to be of 

 very much less importance. Next after the temperatore, however, will 

 be placed the quantity of moisture. {Z. 0. O. M., XIV, p. 219.) 



Hartl has published elaborate study of the observations on terres- 

 trial refraction. Bodega Head, first discussed by Schott in the Coast 

 Survey Keport in 1876. He attempts to deduce some addition to our 

 knowledge of the law of diminution of temperature with altitude. He 

 finally applies Professor Jordan's refraction formula (Astron. Xach., 

 vol. 88), which allows of clearly perceiving the effect of the assumed law 

 diminution of temperature ; he attributes the irregularities of refraction 

 to the temperature changes due to radiation from the soil, and urges the 

 execution of numerous measures of refraction for the better determina- 

 tion of the rate of temperature diminution by the application of Jor- 

 don's formula. {Z. 0. G. i/., XV, 1881, p. 140.) 



Dr. Hamberg, of Stockholm, has studied the apparent transparency 

 of the atmosphere in Upsala, with especial reference to the occurrence 

 of remarkably clear nights and days, when frosts occur injurious to 

 vegetation. From daily observations, from 1 874 to 1877, ot the visibility 

 of objects distant eight or ten miles in the horizon, he deduces the follow- 



