on the Optical Phenomena of the Atmosphere. 7 



True, the radiation in the latter case is likewise more energetic, 

 but not sufficiently so to annul the comparatively great increase 

 of temperature observed upon the glacier. 



The reverse of this must take place when the observations are 

 made immediately over the surface of the bare rocks, where the 

 temperature of the air is known to be considerably heightened. 

 In this case the thermometer placed in the sun could not differ 

 so considerably from that in the shade. This suggests to us 

 the great caution necessary to be observed in experiments of this 

 nature. 



We have also made several observations with a thermometer 

 with a blackened bulb, similar to the photometer of Leslie*. By 

 the pyrheliometer we obtained the increase of the temperature of a 

 quantity of water during an arbitrary unit of time ; while instru- 

 ments of the present description exhibit how far the respective 

 thermometers, in the sun and in the shade, can diverge from each 

 other, and thus furnish results which, in comparison with the 

 former, may be named absolute or maxima differences. In our 

 experiments we used two thermometers, one of which was placed 

 in the shade, and the other, the bulb of which was blackened, 

 exposed to the direct sunlight. Instruments of this description 

 can only be compared with each other f. For the sake of bre- 

 vity we will name the thermometer with the blackened bulb, and 

 which stood in the sun, the photometer. 



Observations with the blackened Thermometer. 



1 



»J 

 3 

 4 

 5 

 6 

 7 

 B 

 9 

 10 



Place of observation. 



Height. 



Day. 



Grossglockner, second peak 12,158 .Aug. 29. 

 Similaun (summit) 11,135 jSept. 13. 



Adlersruhe 



Rachern 



Todtenlocher 



Neve of the great Petz- J 

 thai-glacier § | 



Neve of the Niederjoch.. 

 Gbssnitzthal 



10,432 Aug. 29. 



10,362 



10,340 



8,500 



Sept. 4. 

 Sept. 1 

 Sept. 11.* 

 Sept. 11* 

 Sept. 11.* 

 Sept. 13. 

 Aug. 21. 



Temperature 

 Hour . of the air in 

 the shade. 



h 



1 p.m. 

 12fp.m. 



2 p.m. 

 1 p.m. 



12 



1 p.m. 



2 p.m. 



3 p.m. 

 3 p.m. 



12 



3-2 

 0-8 



10 

 58 

 4-4 

 2-4 

 2-4 

 2-2 

 2-4 



174 



Photo- 

 meter. 



161 

 137 



340 

 173 

 19-2 

 25-0 

 23-8 

 13-6 

 15-7 

 331 



* John Leslie, Short notice of Experiments and Instruments which relate 

 to the Deportment of the Air towards Ileat and Moisture. Leipzic, 

 I-J-. svo. 



f The instrument of Leslie is a differential thermometer with a blackened 

 bulb. It is placed under a glass shade and set in the sun ; notwithstanding 

 tins however, the results raven by different instruments cannot be well 

 compared with each other. Compare Ritchie, lMinhmgh Journal, Se.iii. p. 106. 



% The obserrationa marked thus * arc from 184/1 



§ Noa. C> to '.) inclusive, immediately over the surface of the granular 

 snow ii 



