Dr. C. Davison on Earthquake- Sounds. 41 



records of this kind occur in many earthquakes. For in- 

 stance, during the Hereford earthquake 8J per cent, of the 

 observers who were certainly awake, and heard the sound, 

 state expressly that they were unconscious of any sound 

 while the shock lasted. Generally it was heard only before 

 the shock, ceasing either gradually or somewhat abruptly 

 about the time when the shock began ; but it was sometimes 

 heard only when the shock was dying away, and in two 

 cases before and after, but not during, the shock. That this 

 cessation of the sound was inherent in the observers and not 

 due to their position, is evident from the experiences of 

 others in the same places. At Presteign, in Radnorshire, to 

 one observer the sound ceased before the vibrations com- 

 menced ; to another the sound was terrible, as of rending 

 rocks beneath his feet, and was loudest at the time when 

 the shock was strongest. At Birmingham one observer 

 heard the sound before, during, and after the shock, another 

 entirely before it, a third only after it, while others, as 

 already remarked, heard no sound at all. 



Variability in the Nature of the Sound. — Even when 

 observers in the same place agree in hearing the sound, it 

 may present itself to them under different forms. In the 

 Hereford earthquake we find that at Hereford a crash or 

 bomb-like explosion was noticed during the rumbling sound 

 by four observers, while four others describe the sound in 

 terms which imply uniformity of character. At Pridewood 

 (four miles from the epicentre) one observer, who felt two 

 series of vibrations and heard a loud crash with the maximum 

 of each, remarks that only a few heard this peculiar sound, 

 although most persons noticed a premonitory rumbling. At 

 Ledbury the sound, according to one, began like a rushing 

 wind, and culminated in a loud explosive report; another 

 heard a noise like distant thunder, which ended when the 

 shock began ; while a third heard no sound at all. The same 

 diversity, both in character and intensity, is noticeable at 

 places further away from the epicentre. At Clifton one 

 person heard a slight rumbling noise, while another compared 

 the sound with that of a heavy traction-engine passing. In 

 the Birmingham district the accounts refer ou the one hand 

 to the distant approach of a train and the rising of the wind, 

 on the other to the reports of large cannons and to a noise as 

 if tons of debris had been hurled against the wall of a house. 



Explanation of the above Phenomena. — These observations 

 show clearly that there is a lower limit of audibility, and, 

 further, that this limit is not the same for all persons. Now, 

 to create an equally strong impression on the ear, the 



