MODERN BIOLOGY 315 



Upon the development of natural science, although he did not rise to the 

 highest levels in any particular sphere. As a scientific explorer he is without 

 a rival and he raised geography to the rank of a science. Climatology es- 

 pecially owes its fundamental principles to him: thus, the method of indicat- 

 ing on the map by means of isothermal lines places having a similar annual 

 temperature was invented by him. He devoted many years of methodical 

 study to terrestrial magnetism, and the magnetic-meteorological observa- 

 tories which are now established throughout the globe have him to thank 

 for their existence. As a geologist he deserves especially well of science, 

 owing to his studies of the problem of Vulcanism; he established the fact 

 that the volcanoes exist grouped in ranges along cracks in the earth's crust. 

 But he was also highly interested in biological problems. 



Humboldt' s idea of life- force 

 In his youth he expounded a theory of life as a whole in the form — charac- 

 teristic of the man himself and of his age — of a mythological story en- 

 titled Die Lebenskraft oder der rhodische Genius. The gist of it is that life is 

 maintained by a force that prevents the elements of which the body is com- 

 posed from obeying the laws of affinity that hold good in inorganic nature.' 

 In his old age, however, he abandoned this fantastic theory and in his later 

 writings utters a warning against any kind of speculating upon the life- 

 force. He displayed greater exactitude, however, in his investigations, 

 published shortly before his South American expedition, into the influence of 

 electricity upon muscles and nerves, which he carried out partly with himself 

 as subject, and which, together with a number of natural-philosophical 

 illusions, contain ideas that have been utilized in research work of a later 

 period in connexion with electrical phenomena in the animal kingdom. 



His vegetable geography 

 The greatest service rendered to biology by Humboldt, however, was his 

 creation of vegetable geography. Even as early as in Linnasus we found a 

 lively interest and a keen eye for the life-habits of plants. Linnasus's investi- 

 gations into the question of the habitat and distribution of plants (Part II, 

 p. 115) were, however, based entirely on his classification system. Humboldt's 

 interest in plant life, on the other hand, is at the very outset of quite a 

 different nature. As is the part of a natural philosopher, he takes as his 

 starting-point life in its entirety, examines its various manifestations, and 

 finally dwells on the special advantages which soil and climatic conditions 

 offer to the vegetable world in different latitudes. He puts the question: 

 How is the shape of plants affected by these conditions of life? And he 

 searches for the connexion between the impression made by the landscape 



^ The idea contained in this story is without doubt directly or indirectly influenced by 

 Stahl's previously mentioned theory of the soul as the force that prevents the chemical com- 

 ponents of the body from disintegrating (see Part II, p. 181). 



