A STUDY IN LOCOMOTION. 3 i 7 



being required to remove a foot of surface that solidification by cool- 

 ing must keep pace with it ; 2. Volcanoes are generally not situated in 

 areas of erosion, but along coast-lines and on islands ; and, 3. They 

 are conspicuously associated with lines of fracture and elevation. 



A simple explanation of the phenomena of vidcanism is suggested 

 by the writer, and that is the relief of pressure by slight arching of 

 the crust of the earth along lines of elevation, while the pressure is 

 maximum under the unbroken areas on either side. This unequal 

 pressure would cause a flow of liquid or viscous matter toward and 

 upward under the mountains that mark the lines of arch and fracture, 

 and would permit heated matter held in solidity by pressure to assume 

 the fluid state. 



Mallett's theory, that the arching of plates of the earth's crust, and 

 the arrest of their motion in falling, would generate heat sufficient to 

 liquefy masses of rock, and produce volcanic eruptions, is rejected, for 

 the reasons that the strain on arches of sufficient magnitude would be 

 too great for the resistance of the materials composing them, and as 

 Mr. Fisher argues, the heat generated by this method, even if great 

 enough, would not be localized. 



Mallett's theory wag framed to account for vulcanism in the crust of 

 the earth, on the supposition that the crust was very thick, as claimed 

 by Hopkins, Thompson, and Darwin, but Henessey and Delaunay have 

 clearly shown that the investigations supposed to demonstrate the 

 great thickness of the crust are valueless and irrelevant, as the prem- 

 ises assumed are not those of nature, and that we have as yet no evi- 

 dence of such thickness of crust as would make it impossible for vol- 

 canoes to be fed from a general molten mass below the earth's solid 

 crust. 



In conclusion, we take pleasure in commending the numerous maps 

 and plates which embellish these elegant volumes. No other scientific 

 work known to us has so many, nor any more artistic or better adapted 

 to supplement and illustrate the text. 



I 



A STUDY IN LOCOMOTION* 



Br Professor E. J. MAEEY. 



F the interest of a scientific expositor ought to be measured by the 

 importance of the subject, I shall be applauded for my choice. In 

 fact, there are few questions which touch more closely the very exist- 

 ence of man than that of animated motors those docile helps whose 

 power or speed he uses at his pleasure, which enjoy to some extent his 



* " Animated Motors : Experiments in Graphical Physiology." A lecture delivered 

 at the Paris meeting of the French Association, August 29, 1S78. 



