296 ANNUAL OF SCIENTIFIC DISCOVERY. 



of geological argument, but Professor Rogers looked upon it as belonging to a 

 class of inferences which arc more of the nature of ingenious mathematical 

 exercises on physical problems tlum expressions of the facts or laws of nature. 

 Such problems often involve mechanical conditions too various and complex 

 to be amenable even to the most profound analysis ; so that to bring them 

 . within his grasp, the mathematician is compelled to resort to simplifying 

 hypotheses, and in doing so, departs, often greatly and to an unknown extent, 

 from the actual physical conditions of the problem. Professor Rogers main- 

 tained that conclusions so derived, however true as logical deductions from 

 the premises, are not to be received as demonstrated physical facts. Should 

 the correspondence of earthquake phenomena wilh those of the tides be con- 

 firmed by furtlriT comparisons, to which M. Perrey has been invited by the 

 French Academy of Sciences, it would furnish a proof of the igneous fluidity 

 of the interior of the globe, and of th.3 yielding thinness of its inclosing shell, 

 too conclusive to be weakened by any calculations deduced from hypothetical 

 data. 



Professor Rogers then alluded to the late experiments of Hopkins and 

 Fairbairn, to determine the influence of pressure upon the melting point of 

 solids. As we know that pressure augments the temperature necessary to 

 vaporize liquids, it has become a question of interest, bearing upon the inter- 

 nal fluidity of the globe, to ascertain if it has a like effect upon the tempera- 

 ture at which solid bodies become fluid. According to Hopkins and Fair- 

 bairn, such an effect actually occurs with spermaceti, wax, sulphur, and 

 stearine, but has not yet been detected in certain other very fusible solids 

 experimented upon. Should it prove to be a general law, applicable also to 

 mineral masses, which is yet far from being demonstrated, we should have 

 to admit a higher internal temperature than would otherwise be needed to 

 maintain the interior in a fased state ; but this addition would, most probably, 

 form but a small fraction of the wiiole temperature. In regard to the influence 

 of centrifugal force in causing earthquakes, Professor Rogers remarked that 

 such effect could only arise from a variation of the centrifugal force, and 

 therefore of the earth's velocity of rotation. But the uniformity of this rota- 

 tion is so nearly perfect that a change amounting to even a fraction of a 

 second in a day, would be too startling an occurrence to escape astronomers. 

 Hence, any variations of centrifugal force that may arise must be comprised 

 vriihin extremely narrow limits. Even at the equator, where this force is 

 greatest, its proportion to gravity is very small, and when we consider that 

 any admissible fluctuation of its intensity must be a very minute fraction of 

 the whole force, and hardly more than an infinitesimal part of the force of 

 gravity, the effect of such change, even at the equator, must be regarded as 

 entirely inadequate to those extensive movements, and permanent changes of 

 level, attending earthquakes. 



At a subsequent meeting, a communication was presented from Dr. Winslow 

 of California, who stated that he had recently spent a short time in investigat- 

 ing the geology of Acapulco, Mexico, and the earthquake phenomena, of 

 which that place is peculiarly the focus. He states that he found that the 

 shocks were more numerous there as winter approaches, and during December 



