4 2 4 NINETEENTH CENTUKY. PT. ill. 



he was ninety years of age. In the sixty-six years between 

 these two dates he collected and published in popular 

 language an immense number of facts about nature in all 

 paits of the world. 



His chief voyage was to America in 1799, when he spent 

 six years in Mexico, and along the shores of the Orinoco in 

 the Andes. Here he began one of his greatest undertakings, 

 namely finding out the climate of different parts of the 

 world, and tracing out isothermal lines, or lines of equal 

 heat over the globe, showing what countries have the same 

 average temperature, and explaining why some enjoy an 

 almost equable climate all the year round, while others are 

 very hot in summer and cold in winter. For example, he 

 pointed out that Greenland is much colder than Lapland, 

 even in places which are on the same line of latitude, 

 because a cold current from the North Pole flows past 

 Greenland, while the warm Gulf Stream crosses over from 

 the Gulf of Mexico and washes the shores of Lapland. The 

 importance of this study of variations of temperature was 

 first pointed out by Humboldt, and it should be remembered 

 as one of his most original investigations. 



Again, in his long journeys through South America, he 

 traced everywhere the different species of plants which 

 grew at various heights, even up to 20,000 feet on the slopes 

 of the Andes. This led him to try and find the reasons 

 why certain plants are only to be found in certain areas, in 

 the same way that Buffon had worked out the distribution of 

 animals. When he returned to Paris in 1 804 he had col- 

 lected an immense number of facts as to the heights of 

 mountains, the climate of countries, the minerals and metals 

 found in them, the active and extinct volcanoes, the nature 

 of the rocks and soils, the vegetation and the animals ; and 

 with the help of the best scientific men in Paris (each 



