1823.] Crystalline Forms of Artificial Salts* 121 



Fig. 1. ^»^-^ 



Fig. 2 represents one of the varieties of intersected crystals 

 which occur very frequently among the single ones, the nature 

 of which will be readily understood from the similar letters 

 placed on the corresponding planes. 



M on M' 107° 26' 



M on /; \ lOQ /ro 



M' onb'f ^^"^ ^"^ 



Mon ^ 126 17 



hone 119 43 



conc\ 120 34 



c on the lateral plane 



c'fig.2 119 43 



Article VII, 



On the ComtitiUion and Mode of Action of Volcanoes, in differ^ 

 ent Parts of the Earth, By Alexander Von Humboldt.* 



When we consider the influence which scientific travels into 

 distant regions, and a more exteiided geographical knowledge, have 

 for some centuries past exerted upon the study of nature, we soon 

 discover how this influence has varied according to the objects of 

 inquiry, which have been, on the one hand, the forms of the organic 

 world, and, on the other, the inanimate formation of the earth ; — 

 the knowledge of rocks, their relative ages, and origin. Differ- 

 ent forms of plants and anirnals enliven the earth in every zone, 

 as well in the plains, where the heat of the atmosphere is deter- 

 mined by the geographical latitude and the different inflexions of 

 the isothermal lines, as where it changes suddenly on the steep 

 declivities of the mountains. Organic nature gives a peculiar 

 physiognomical character to every zone, which is not the case 

 with the inorganic world where the solid crust of the earth is 

 divested of its vegetable covering. The same rocks approaching 



Read before the Royal Academy of Sciences of JBeilui; Jan. S4, 1823. 



