Dr. C. Davison on Earthquake- Sounds. 31 



and 3 per cent. This seems to show that in the cases of some 

 sheets of hard rubber, the thermal conductivity of the skin 

 near the polished surfaces is somewhat less than that of the 

 mass of the material in the sheet. This difference, however, 

 is too slight to account for the differences of conductivity 

 shown by the table. It is well to emphasize the fact that the 

 specific heat between 25° C. and 100° C. of the standard 

 rubber is less (0*339) than that of such thin sheet rubber as 

 I have experimented upon. 



Stefan found for the thermal conductivity of a certain 

 sheet of rubber, 0*787 centim. thick, the value 0*00026: this 

 rubber had a somewhat greater density (1*22) and a much 

 lower specific heat (0'23) than any of my specimens, so that 

 the ratio of the conductivity to the specific heat per unit 

 volume was somewhat greater. Experimenting upon a small 

 disk of " ebonite " 1*93 centim. in diameter and 0*0414 centim. 

 thick, Lees found the conductivity to be 0*00040. 

 The Jefferson Physical Laboratory, 



Harvard University, Cambridge, U.S.A. 



III. On Earthquake- Sounds. 

 By Charles Davison, Sc.D., F.G.S.* 



IN a short paper published seven years ago f, I attempted 

 to describe the phenomena of earthquake-sounds and to 

 offer a theory of their origin. More detailed studies of 

 recent British earthquakes, and especially of the Hereford 

 earthquake of 1896, have added to our knowledge of the 

 phenomena and slightly modified the theory. The catalogues 

 of foreign seismologists have also furnished materials for in- 

 vestigation. I propose therefore to reconsider the subject in 

 the present paper, dwelling chiefly on those points which 

 have not yet received much attention. 



General Character of the Sound. 



The earthquake-sound is frequently described simply as a 

 rumbling sound or, more fully, as a hollow or muffled rumbling- 

 sound, a harsh grumbling sound, a mysterious suppressed 

 roar, or a strange deep sort of groan or moan. Occasionally, 

 sounds of a totally different kind are observed, either alone 

 or in conjunction with the preceding, sounds that are de- 

 scribed by the terms rustling, whizzing, or hissing. The 

 sound is generally of a more or less jarring nature, hardly 

 ever becoming a musical tone, although it may approach to 



* Communicated by the Author. 



t " On the Nature and Origin of Earthquake-Sounds ": Geol. Mag. 

 vol. ix. 1892, pp. 208-218. 



