38o 



NOTES OF A NATURALIST. 



world where the daily range of temperature near the coast is 

 very slight, we may with small risk of error use the mean 

 temperature of the season at the lower station as the element 

 of comparison, and, in places near the equator, the mean 

 annual temperature. For this reason, observations in the Andes 

 of Ecuador, Peru, and Bolivia present great advantages, and I 

 think it may be useful to discuss the results so far as they are 

 now available. 



It is scarcely necessary to examine critically the results of 

 the earlier explorations. Humboldt has given in the " Recueil 

 des Observations Astronomiques," etc., and in the " Memoires de 

 la Soci^t^ d'Arcueil," vol. iii. p. 579, and elsewhere, the observa- 

 tions made by himself in Mexico, Colombia, and Peru, and also 

 those of Caldas and Boussingault, and has derived from them 

 a table which, with more or less modification, has been adopted 

 in many physical treatises. It exhibits the mean difterences of 

 temperature found in successive zones differing in height by 

 500 toises, the interval corresponding to 974'6 metres, or very 

 nearly 3000 English feet. 



The first remark to be made about this table is that the 

 observations on which it is founded are not properly comparable, 

 being partly single observations made during an ascent, and 

 partly the mean of numerous observations made at certain 

 places, such as Mexico, Quito, etc. It may further be remarked 

 that many of the heights determined by Humboldt have been 

 considerably modified by the results obtained by more recent 

 travellers, and cannot now be regarded as correct. The influence 

 of plateaux is, however, very apparent, as nearly all the observa- 



