498 proceedings: philosophical society 



The final paper by Messrs. E. F. Mueller and M. S. Van Dusen, 

 on Heat of combustion of volatile liquids, was presented by Mr, MuELLER. 

 The paper was illustrated by lantern slides and the burner used by the 

 authors was exhibited. Messrs. FooTE and Sosman discussed this paper. 



83 1 ST meeting 



The 831st meeting was held at the Cosmos Club March 13, 1920, 

 with President Sosman presiding and 60 persons present. 



The first paper was by Mr. E. D. Williamson on Earthquakes and 

 the elastic properties of the earth. 



Data from geographic and astronomic sources have established some 

 qualitative measure of the earth's rigidity, average density, and the 

 distribution of the earth's mass. Earthquake records, properly in- 

 terpreted, give us an immediate check on the conclusions which have 

 been reached. 



Two of the types of waves propagated as the result of a seismic dis- 

 turbance travel through the earth with velocities in each case inversely 

 proportional to the square root of density but depending in one case 

 on the rigidity and in the other on both the compressibility and rigidity. 

 It is necessary then to find the relation of the velocity of the wave 

 to the depth beneath the surface of the earth to get further information 

 as to the variation of these other quantities. Wiechert at Gottingen 

 first solved the problem by graphical means, but since then more direct 

 analytical methods have been developed to find from a transit-time 

 curve, the path of the wave through the earth and its velocity at var- 

 ious points. 



The results to which the writer and L. H. Adams were led by their 

 investigations are outhned in the second paper, presented by Mr. L. H. 

 Adams on The nature of the interior of the earth. It has long been known 

 that since the average density of the earth (5.5) is so much higher than 

 the density of ordinar>^ surface rocks, the central portion must have a 

 very high density — probably lo.o or more. To account for this in- 

 teresting fact we may assume either that the center of the earth is 

 composed of relatively hea\'y forms of matter or that the extreme 

 pressures in the interior — two or three millions of atmospheres — have 

 compressed the ordinary rock material to one-third to one-quarter of its 

 original volume. With regard to the second hypothesis, we have 

 no information to guide us in forming an opinion concerning the behavior 

 of matter at these enormous pressures so far beyond the range of labora- 

 tory experimentation. Fortunately, however, the data on the propa- 

 gation of distant earthquakes may be made to shed some light on this 

 important question. Starting with the known velocity v of the trans- 

 verse vibrations at the distance r from the center of the earth, the 

 density p produced by cotnpression alone may be calculated by graph- 

 ical integration and successive approximation, using the equation : 



log, ^ =hC 

 Po J r 



Po J r^ r^ v^ 



