32 Dr. C. Davison on Earthquake- Sounds. 



such a character, as is evident from the comparisons to the 

 deep notes of an organ, &c. The references to distant 

 thunder and the moaning of the wind also testify to a certain 

 smoothness or monotony in the sound. To some observers, 

 however, the sound appears to be intermittent, to be like 

 three loud explosive moans, or successive discharges of 

 cannon, or a heavy body falling several times, say, down a 

 short flight of stairs. 



At places near the epicentre, the loudness of the sound is 

 one of the chief features of a moderately strong earthquake. 

 The sound is compared to the rumbling of six traction-engines, 

 to that of a train going over a bridge, only intensified a hundred 

 times, to a tremendous roaring, a sudden loud deafening 

 noise, or a terrific explosion, louder than is produced by the 

 heaviest artillery. Even in so slight an earthquake as that 

 felt in the south of Cornwall on April 1, 1898, one observer 

 described the sound as like the rumbling of thirty or forty 

 waggons travelling at a rapid pace, while another remarked 

 " that w T as the loudest thunder I ever heard." This may 

 almost appear to be the language of exaggeration ; but, from 

 a careful study of the evidence, I think that it expresses the 

 experience of certain, but not of all, observers. It will be 

 seen afterwards how widely persons differ in their powers of 

 hearing earthquake-sounds. 



Another prominent characteristic of the sound is its extra- 

 ordinary depth. The rolling of heavy railway-trucks, very 

 low, is the evidence of one observer ; of another, a low 

 rumbling sound, much lower than the lowest thunder ; while 

 a third refers to the vibrations of the pedal notes of a great 

 organ, only of a deeper pitch than can be taken in by the 

 human ear. The idea of great depth is also given by the 

 very frequent use of the word " heavy "*. It is applied in 

 every type of comparison, sometimes in an unusual manner, 

 as, for example, in heavy thunder, a heavy conflagration, or 

 a heavy explosion. 



The earthquake-sound is frequently compared to the passing 

 of heavy waggons and other vehicles. The comparison seems 

 to be generally suggested when the sound is of long duration, 

 of a certain smoothness, and gradually increases in intensity 

 to a maximum and then dies away t- The reference is often 



* In strong earthquakes, the percentage of descriptions in which the 

 word " heavy " occurs, varies from 28 in the Hereford earthquake of 

 1896 to 45 in the Pembroke earthquake of 1893. In very slight earth- 

 quakes it may fall as low as 13. 



f In the Leicester earthquake of 1893. 27 observers stated that the 

 sound gradually increased in intensity and then died away ; and of these 

 20 compared the sound to that of passing vehicles. 



