8 Dr. H. Schlagintweit's Observations in the Alps 



The days chosen were all very clear. The least shading of 

 the heavens by clouds is, however, capable of causing such con- 

 siderable changes in the maxima of insolation, that a relation 

 between the latter and the height is not to be given with cer- 

 tainty. The temperatures given by the photometer are, however, 

 in the first place, deserving of some attention, because the dark 

 rocks and the most elevated accumulations of earthy matters 

 exhibit similar temperatures very often. They attain sometimes, 

 even at considerable elevations, a temperature from 20 to 30 

 degrees, and again sink under zero by the radiation at night. 



Experiments on temperature in the direct sunshine which are 

 made with the hcliothermometer of Saussm-e*, are comparable 

 with each other only so long as the same instrument is used. 

 The thickness and transparency of the glass, the space of the 

 cylinder, the conductive power of the material, the more or less 

 air-tight closing, &c, are generally very different in different in- 

 struments. It will therefore be sufficient, in the present case, 

 to exhibit briefly those experiments which we made on the Johan- 

 nishiitte (7581 P. F.). We placed the instrument generally 

 from 10 o' clock in the morning to 4 o'clock in the afternoon 

 in the sunshine ; after this hour there was no further increase of 

 temperature observable. 



We obtained — 



I. 40° C. with 6°7 C. 

 II. 35 ... 5°1 ... 



III. 48 ... 7°-9 



IV. 31 ... 5°2 



V. 49 ... 5°-8 



temperature of air in the 

 shade f. 



The radiation also varies with the height ; it becomes more 

 energetic as we ascend. The experiments on radiation were 

 made with a Rumford's minimum, which was placed upon a 

 layer of down and left uncovered. The down served to prevent 

 any lateral conduction of heat to the instrument. This is Poml- 

 let's arrangement J. The observations were made upon Johan- 

 nishiitte in Heiligenblut. The minimum temperature of the 

 night air was observed at the same time as the radiating instru- 

 ment. (Column 4.) 



* The instrument consists of a wooden box, which is blackened inside, 

 and in which the bulb of the thermometer is placed. It is closed above by 

 three glass plates. Fourier has given the experiments made by Saussure 

 with this instrument in his investigations on obscure heat. Mem. del' Acad, 

 des Sciences, Paris, vol. vii. p. 585. 



t Saussure saw his instrument upon Mount Cramont rise to 87° ( '•■ 

 the temperature of the air at the time being 6 0, 2 C. — Voyages, §. 932. 



\ Comptes Rendus, vol. vii. 1838, p. 56. 



