on the Optical Phenomena of the Atmosphere. ' 



Collection of Night Temperatures with and without Radiation. 

 7581 P. F. 1848. 



The last column but one contains M— It, that is, the tempe- 

 rature of the air on Johannishutte minus the results of the 

 radiation thermometer. The contemporaneous maximum of ra- 

 diation in Heiligenblut, at a height of 4004/, amounted to 5 0, 2 C. 

 In the peculiarly clear nights, Nos. 3, 1 and 5, the radiation 

 was nearly constant, varying only from 7'9 to 7*0. As the 

 minimum of the air varied from +5 - 0to — 3T, we may con- 

 clude that the differences in the temperature of the air have no 

 influence upon the radiation. Similar results have long served 

 to support the assumption of the intense cold of the planetary 

 spaces, in comparison with which the differences of temperature 

 observed on the earth's surface almost vanish. It is very diffi- 

 cult to fix upon proper nights for such observations, the latter 

 are so often disturbed by light clouds or by the morning fog. 

 At still greater altitudes, the temperature of the air and the 

 results given by the radiation thermometer differ from each other 

 still more. Martins and Bravais, during their ascent of Mont 

 Blanc, found the following differences on the Grand Plateau : — 



These observations also were made with a thermometer placed 

 upon down. 



Different substances exposed at night exhibit different powers 

 of radiation. The temperature which they assume depends, in 

 a great degree, as well upon their constitution as upon their 

 form. This difference exhibits itself very evidently in nature, 

 particularly in the case of plants. In connexion with this sub- 

 ject we give the following extract from the exceedingly careful 

 investigation of Glaisherf, which refers to various and very cha- 



* Monit. Univers., 1844, p. 2796. 



t " On the Amount of Radiation of Seat at night from the Earth, and 



