5260 Observations on Humboldt's Works 



line exists, a mean temperature of +1:5*; whereas the ut- 

 most reach of trees in Lapland extends to 500 toises, and the 

 snow-line to 550 toises, above the surface of the sea, although, 

 as already mentioned, the mean temperature at the level of the 

 sea is below 0°. This point cannot easily be proved theoreti- 

 cally ; for the mean temperature of the year is partly deter- 

 mined by the temperature of winter, and that has no influence 

 whatever upon vegetation. 



Now although M. Humboldt admits that this f, and many 

 other comparisons instituted by him J, and likewise various ob- 

 servations made in the following parts of the treatise §, afford 

 proof of the above ; he, nevertheless, employs more signs of 

 mean temperature in his comparative views of vegetation in dif- 

 ferent countries. This is the case, for example, in the above- 

 mentioned parallel between North America and the old conti- 

 nent, from p. xxvi. to p. xxix ; likewise in the table, p. xviii-H, 

 p. X. xvi. xix. and 36, and in part p. Iv. In other places he uses 

 a different measure (maastabes), for instance p. xi. and xxx. and 

 in part p. Iv. and Ivi., the mean temperature of the year and the 

 temperature of summer are used ; p. xlii., and likewise in the 

 smaller treatise, the difference between the summer and winter 

 temperatures ; p. liv., the annual mean temperature, and the 

 sum of the temperature of those months, the mean temperature 

 of which exceeds 0°; p. xliii., the mean temperature of the 

 year, and that of the hottest and coldest months ; p. xlix., the 

 annual mean temperature, and the mean temperature of winter, 



*See p. xlix. 



t Pag. xliii. and liv. 



X Pag. xxix. to xxxii. 



§ For example, p. xlvi. xlviii. and liv. 



II It is also surprising that in this table for the equatorial zone, only one 

 fixed mean temperature of 27°. is given, and not, as in the two other zones, 

 a maximum and minimum. Now although the mean temperature from the 

 equator to the tropics appears to decrease less than beyond the same, yet 

 we cannot admit that it is the same at either of the tropics as under the 

 equator. However, p. xxxiv., he ascribes to the equator a mean tempera- 

 ture of 30°. ; and, p. xxix. and xxxix., to the Havannah (23° 8' of latitude) 

 250 Q> J to Vera Cruz ; (19° 11' of latitude) 2.-,o 4' 



