READINGS OF NATURE. 413 



as we may term them, which the venerable pliilosoplicr chaptkr 

 has acliieved by tlie careful study of the phenomena ^'^^ 

 presented to his observation. The interpretation is not Differenrc <>t 

 indeed to be accepted entirely as an established law. 

 Various opinions have been advanced to account for the 

 internal heat of the planet, and its increasing tempera- 

 ture at various depths below the surface. Not the least 

 important or curious of these relate to the mysterious 

 principle of magnetism. Changes of temperature, it is 

 now well ascertained, do call forth magnetic and electric 

 currents ; but the phenomena exhibited by terrestrial 

 magnetism are still only very partially understood, and 

 these, as well as many other great natural laws, must 

 await the labours of others for their complete elucida- 

 tion. They bear, however, to an extent of which we Magnetic 

 , . ^1 1 • , cuirenU. 



are yet only very imperiectly aware, on the nnportant 



subject elucidated by our author in his" Researches on 

 the Causes of the Inflexion of the Isothermal Lines ;"' 

 and which he has extended as an addition to a previous 

 valuable " Memoir" on the same subject. Some of the 

 important views indicated in these Researches have been 

 traced on a previous page. But the entire treatise is of 

 the utmost value to the natural philosopher, as well as 

 of direct practical worth in relation to many depart- 

 ments of our modern political economy. It contains the Practical 

 most important exposition of philosophic views on cli- 

 mate and the distribution of temperature which have 

 ever been set forth by any single individual. The full 

 value of these researches are still very partially appre- 

 ciated, and they have yet almost wholly to be turned to 

 their full practical account in relation to navigation, 

 agriculture, colonization, and the various economic forms 

 to which the researches of the profound observer are re- 

 ducible for the amelioration and progress of his race. 



Such is a slight sketch of Baron Humboldt's Researches 

 in Central Asia, and of some of the valuable facts and 

 important deductions which have already resulted from 

 his labours. Many of his speculations are too profound, 



