338 Henry Woodivard — On Volcanos. 



Here is a diagram to illustrate and answer this question. (Fig. 1.) 



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Fig. L— Height and Depth. 



EXPLANATION OF DIAGEAM. 



A, Atmosphere taken at 50 miles. 



c. Half the pressure of which is shown at five miles. 



d. Mount Everest, the highest known land of the world in 

 the Himalayas, 29,000 feet. 



a. Deepest mines, Himmelfurst in Saxony, 2,400 feet; 

 one shaft in Belgium, 2,796 feet; Dukinfleld 

 Colliery, 2,820 feet.i 



b. Highest balloon ascent, Messrs. Glashier and Coiwell, 

 1862— 6i miles. 



e. Deepest sounding in the ocean, Lat. 36° 49' S., Long. 

 37° 6' W. Soundings were found at a depth of 

 7,706 fathoms, or 8| miles. (A. Keith Johnston's 

 Physical Atlas.) 



. /./. Sea Level. 



From/, to Ic. represents a vertical depth of 50 miles. 



Melting point of iron, or 2,786° Fahr., a heat sufficient 

 to fuse almost every known substance. This calcu- 

 lation is founded upon the assumption that the 

 known increase of 1° Fahr. for every 65 feet of 

 depth, is continued downwards for an indefinite 

 distance. Such an assumption would admit of a 

 solid crust upwards of 30 miles in thickness. 



1 E. Hull, F.R.S., Coal-fields, Quart. Journ. Science, January, 1864. 



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