OF BAEOX HUMBOLDT. 33 



founded upon his researches into the territories 

 of meteorology, the conditions of heat and elec- 

 tricity ; the distribution of heat upon the earth, 

 in so-called isothermal lines, by which he con- 

 nected all places upon the surface of the earth 

 which have an equal medial annual temperature, 

 which proved that the equator of heat the line 

 which one discovers in connecting the hottest 

 points of the earth one with another in nowise 

 harmonizes with the earth-equator ; wherefore 

 those parts of the globe situated near the 

 equator, and having the rays of the sun per- 

 pendicular, are not always the hottest. 



These isothermal lines form an important 

 part in Humboldt's scientific researches ; and 

 more especially in his maturer years, the study 

 of this branch of science was a very favourite 

 pursuit. Already, in 1817, when he published,, 

 in the third volume of the French journal, his 

 " Memoires d'Arcueil," a part of the treatise 

 " de la Distribution de la Chaleur et des Lignes 

 isothermes, 55 he had been long engaged with the 

 distribution of heat upon the earth, and had 

 endeavoured to fix more accurately the direc- 

 tion and form of the isothermal lines. Thus, 

 ten years later, on the 3rd of July, 1827, he 

 delivered a lecture at the public seance of the 

 Academy of Science " respecting the principal 



D 



