230 PROGRESS OF METEOROLOGY IN 1889. 



T the absolute temperature. He believes that this formula will hold 

 good for all temperatures between the meltiug point of ice up to the 

 melting poiut of platinum, while Stefan's law gives results too high 

 for low temperature and much too low for high temperatures. 



Herr Graetz ( Wiedemannls Annalen, 1889, p. 857) criticises Weber's 

 claims, and maintains that Stefan's formula has a much better basis 

 IV, than this new formula. {Meteorologische Zeitschrift, 1889, VI, p. 38.) 



Laws of thermal radiation. — In an article on the law of the thermal 

 radiation, Professor Ferrel has compared with observational data, both 

 Duloug and Petit's law and Stefan's law of radiation. He finds that 

 Dulongand Petit's law holds through only a comparatively short range 

 of temperature, and the same is true of any function of the same general 

 form ; but by giving different values to the constant in the formula 

 (taken by Dulong and Petit as 1.0077), increasing with lower tempera- 

 tures, the rate of cooling may be represented through a considerable 

 range of temperature. For temperatures from 50° C. to 137° C 

 Stefan's law agrees with the observed rates of cooling, but for higher 

 temperatures an exponent of 4.2 is required instead of 4. 



Professor Ferrel then shows that the law of radiation for the result- 

 ant radiation of all wave lengths must diff'er very much in different 

 bodies in which the radiativities differ considerably from that of a sur- 

 face of maximum radiativity, according as the predominating wave 

 lengths in the radiations are toward the one or the other end of the 

 spectrum. The application of the various radiation formula? in obtain- 

 ing the temperature of the sun is shown to give no reliable results. 

 {American Journal of Science, xxxviii, p. 3.) 



V.-SOLAR RADIATION AND ATMOSPHERIC ABSORPTION; TEMPERATURE. 



Solar radiation. — During the summer of 1888 a series of observations 

 of solar radiation were made on Mont Ventoux (altitude 1,907 meters) 

 with a continuously recording photographic Crova actinometer. The 

 following is a brief statement of results : 



Continual oscillations are apparent in the solar curve, but with a 

 smaller amplitude than at Montpellier. 



A regular midday depression of the curve takes place to the same 

 degree as at Montpellier. This is due to the vertical ascent of vapor, 

 and not to the influence of the sea. 



The solar constant, computed from the observations at Montpellier, 

 is nearly 3 calories, and it is believed that the registering apparatus 

 and the method when used at greater heights will give a value greater 

 than 3 calories. 



The polarization of the sky-light appears as a rule to be greater the 

 greater the solar constJint and the smaller the diathermancy. Conse- 

 quently the degree of polarization may furnish useful indications for 



