ISOTHERMAL PHENOMENA. 405 



the moon. We are therefore confirmed in the value to chapter 

 be attached to illustrations and elucidations of terrestrial "^^^''^^^ 

 phenomena, derived from those which are discoverable in Value of 

 its attendant satellite ; and though some of those most enceZ'^''^'^ 

 recently advanced may be open to dispute, we cannot 

 doubt that further observation will lead to still greater 

 revelations of truth, in relation to those astonishing x-e- 

 volutions on our own planet's surface, which supervened 

 while yet " the earth was without form, and void, and 

 darkness moved on the face of the deep." 



The third and concluding volume of Humboldt's Phiiosopiii.- 

 "Researches in Central Asia," enters into questions no '"^^'•''*"^ '''^• 

 less 'interesting to the natural philosopher than those 

 which precede it ; though it is not easy to reduce to an 

 abridged and popular form the original views, and numer- 

 ous new and important facts and observations, which 

 arri embodied in it. It includes " Considerations on the 

 Temperature and Hygvometrical state of the Air, chiefly 

 in Asiatic Russia ;"' " Researches on the Causes of the 

 Inflexion of the Isothermal Lines ;" " On the Magneti- 

 cal Inclination observed in Russia in 1829, and on the 

 Peculiar Phenomena observed in the Climate of that 

 country." It also includes a section on tlie " Routes in 

 Central Asia." All of these embody many valuable and 

 important observations, and those which specially refer 

 to climate and the distribution of heat, embody an amount 

 of original views and observed facts, such as no other in- 

 dividual has ever brought to bear on these important 

 subjects. To these observations, indeed, we owe the esta- 

 blishment of many of the most important recognized 

 meteorological laws, as well as the establishment of an Meteorolnrf- 

 isothermal system applicable to the whole globe, and 

 resting mainly, not on theory, but on well-ascertained 

 data. The result of these may be thus briefly reduced 

 to an abstract. The isothermal lines, or the lines of 

 equal annual mean temperature over the globe, vary 

 very considerably from the parallels of latitude, and de- 

 viate with much irregularity in different countries, so 

 2 B 



