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



made at midday, between 12 and 1 o'clock. The 4th of September 

 1848, on which the observations on the Rachern (10362 P. F.) 

 were made, seems to have been a peculiarly favourable day. It 

 was not only entirely cloudless, but its transparency, when the 

 distant alps were observed, was very striking ; on this day the 

 difference between the sunned and shaded thermometer was un- 

 usually great. 



The observations on the Rachern gave as follows : — 



Time of observation, Sept. 4, 1848, l h 10 m p.m.* 



Height in Parisian feet 



Reduced height of barometer in millimetres . 



Temperature of the air 



Teroperatxire of the water at the commencement . 

 Temperature after five minutes' radiation . 

 Temperature after five minutes' exposure to the sun 

 Temperature after five minutes' further radiation 



Increase for five minutes without radiation . . 5°"75 



The maximum of the increase obtained by Pouillet f, after the 

 elimination of the radiation, was5 0- l C. (Paris, May 11, 1838,12 h ). 



The insolation was also determined by observations made with 

 two thermometers ; one of which was set in the sun, and the 

 other, in the usual manner, in the shade. Lambert J, Alexander 

 von Humboldt §, De Gasparin||, and Quetelet^f, have pointed 

 out the import of such determinations, and the two latter have 

 applied the method in a long series of experiments. 



We here communicate a number of insolations which we have 

 had opportunity to observe. They are the results of single ex- 

 periments; and perhaps, even as separate phsenoinena, on ac- 

 count of the considerable elevation to which they refer, are 

 deserving of some attention. 



* The insolation at 12 o'clock might be taken at something over 5'8. 



t For the limit of the atmosphere, the observations of Pouillet made at 

 different hours of the day gave 6° - 27 C. If we omit to compare our obser- 

 vations with those of Pouillet, and the similar ones made by Ka:mtz and 

 Forbes with Herschel's actinometer, our apology is, that for these investi- 

 gations numerous observations are necessary, as the single observations are 

 so liable to disturbances from the altered serenity of the sky. 



X Lambert, Pyrometrie, § 283 ; Photometrie, § 886. 



§ Alexander von Humboldt, De Distributions Plantarum, 1813, p. 167. 



|| De Gasparin, Cours d' Agriculture. 



IT Quetelet, Instruction sur V observation des ph&nomenes p&iodiques, and 

 Sur le Climat de la Belgique, chap. 4. 1846. From the Annates de I'Ob- 

 servatoire de Bruwelles. 



