10 Selim Lemström. 



un this phenomenon attention has been fixed only in later times by re- 

 searches of Mr E. Russel ' and Herr Wollny ^. 



By experiments I hâve earlier sought to form an idea on tlie surface of 

 the eartli as a source of heat, and I will mention hère the most important. 



The actinometric experiments in general are not as sure as would be dé- 

 sirable, but one case makes an exception. If a therm om eter be laid on the 

 ground in such a manner that only the tube, not the bulb, touch it i. e. 

 that the bulb lie free 1 or 2 cm above the surface, this thermometei' must 

 clearly give the température l'esulting from the différence of heat radiating 

 from the bulb into space and the heat radiating to it from the earth [See 

 Note II]. 



As the conditions of thèse experiments are exactly defined and therfore 

 the results sure, it may also, through a little change, serve to give an approxi- 

 mate value of the intensity of radiation from the surface of the earth. If two 

 thermometeis of the same kind A and B be placed near each other in the 

 manner described above and one of them B be covered witli a leaf, the la- 

 diation to space must surely be diminished. In case that radiation from the 

 surface of the earth should be worth noticing, the température of B will 

 rise and its sui'plus över A ought to be an approximate measiu'e of its in- 

 tensity. 



Similar experiments were made by me as early as 1880, hut they liave 

 since then been repeated and have always given the same results. 



I will only mention the following: 



June 15"' 1880 (Table III) 



Biill) of thermometei 



Med. -0,1 



A remarkable circumstance in this experiment is that the covered thermo- 

 meter in the most cases shows a lower température than the uncovered one. 



' Dew and Frost. Nat. Dec. 1892 p. 210. 

 2 Forschungen etc. il). Febr. 1893 p. 398. 



