356 ALEXANDER VON HUMBOLDT. 



work (see p. 349). and the pressure of a voluminous corre- 

 spondence which consumed a considerable amount of time, he 

 read the following papers before the Academy :* c On the Laws 

 regulating the Decrease of Temperature in the Higher Be- 

 gions of the Atmosphere and the Limit of Perpetual Snow ; ' 

 ' On Steppes and Deserts ; ' ' On the Cataracts of the Orinoco ; ' 

 4 Thoughts on the Physiognomy of Plants.' Several smaller 

 treatises, of which he made presentations to the editors, ap- 

 peared in various periodicals. Among these may be cited : 

 ' On the Aboriginal Inhabitants of America ; ' ' Experiments 

 upon Electrical Fish ; ' ' Upon the Various Species of Cinchona ; ' 

 6 Capture of Electric Eels by means of Horses ; ' c Observations 

 on the Influence of the Aurora Borealis upon the Magnetic 

 Needle, instituted at Berlin on the 20th of December, 1806 ;' 

 6 On the Scientific and Mathematical Instruments devised by 

 Nathan Mendelssohn,' 1 &c. 



Labours of a purely experimental character also occupied 

 the attention of Humboldt ; at this time he commenced a 

 series of observations upon the earth's magnetism, at first, in 

 conjunction with Gray-Lussac, which were carried on in a small 

 building constructed for the purpose entirely without iron in 

 the garden of Herr George, a wealthy brandy distiller, a site 

 now occupied by Renz's Circus. Varnhagen remarks in his 

 journal, on July 4, 1857: 'Humboldt was relating to me 

 yesterday that when he was carrying on magnetic observations 

 in an out-building in Greorge's garden, he was at one time so 

 intently occupied in his labours that he spent seven days and 

 nights in succession with only snatches of sleep, as every half- 

 hour he had to take the readings of the instrument ; subse- 

 quently he was relieved in this duty by his assistants. This was 

 in 1807, just fifty years ago : I have often seen this building 

 when visiting Johannes von Muller, at the time he too was 

 conducting observations in a garden-house. Humboldt further 

 related, that when Greorge, as an old man, used to show strangers 

 over his garden, he never failed to boast of "his scientific 

 friends." u Here I used to have the famous Muller, here Hum- 



1 Nathan Mendelssohn, the youngest son of Moses Mendelssohn, was an 

 admirable mechanician, and one of the most zealous founders of the 

 Polytechnic Society of Berlin ; he died in January 1852. 



