On the Passage of the Galvanic Current through Iron. 217 



where r is the radius of the mountain at any distance x from 

 the vertex, and N the modulus of rigidity. 



Now if a is the radius of the base, then at any distance x from 

 the vertex the radius is 



x 



Assuming, as before, that N is equal to one third of E, we have 

 for the deflection produced by the horizontal force acting at the 

 centre of gravity of the mountain 

 ■* 2>Vdx 



A 



77 T? a 



or 



Consequently 



3PA 



27ra 2 E' 



T=2tt x /K w 

 V 2a. 



2gE 

 = 0*00107 x h approximately. 



Hence a cone in which the diameter of the base is not much 

 less than its height makes a complete vibration in one second 

 if its height is 1000 feet; and the times of vibrations of such 

 cones and pyramids are proportional to their heights. 



A large cone, however, would not receive the earthquake- 

 shock as a house does, because the house receives the vibra- 

 tion at every portion of its base almost simultaneously; so 

 that it is difficult from the equation concerning the vibrations 

 of buildings to predicate the production of cracks at the base 

 of mountains. In fact, the question must be treated in a dif- 

 ferent way, the propagation of vertical and horizontal strains 

 being considered. It is evident, however, that unless the 

 earthquake is of a suddenness such as we cannot comprehend, 

 no fracture will be produced at the base of a hill or pyramid 

 of, say, 100 feet in height. 



XXV. On the Passage of the Galvanic Current through Iron. 

 By Felix Auerbach, Ph.D., of Breslau. 

 [Continued from p. 152.] 

 § 8. ~YTTE have yet to reply to the question ivltetlier the theory 

 * ▼ above sketched conditions an influence upon the fun- 

 damental laws of galvanism, as well as upon the galvanic constants 

 of iron, and, in the case of an affirmative answer, how this 

 influence asserts itself. 



