84 



KNOWLEDGE. 



[Apbil 2, 1900. 



driven rapidly over stone paving or on a hard or frosty 

 road ; express trains or heavy goods trains rushing over 

 an iron bridge or through a tunnel or cutting ; or 

 weighty furniture dragged along the floor. (2) 

 Next in frequency come comparisons to thunder, occa- 

 sionally to a deep peal, but most often, perhaps, to 

 distant thunder. (3) In some earthquakes, but by no 

 means in all. the sound appears to resemble a rough or 

 moaning wind, the howling of wind in a chimney and 

 a chimney on fire. (4) When it is of short duration 

 and fairly uniform in intensity, we find the sound 

 described as like that of a load of coal or bricks falling 

 from a cai-t, or of a wall or roof tumbling down. (5) Again, 

 when still briefer, it is compared to the thud of a pon- 

 derous weight, a large mass of snow or of heavy timber, 

 or the slamming of a door. (6) In weak earthquakes, 

 and above all in the slight after-shocks of a great earth- 

 quake, we have references to explosions of different 

 kinds, but chiefly to colliery explosions, rock-blasting or 

 the firing of artillery, especially when they occur at a 

 distance. (7) Lastly, there are several descriptions of 

 a miscellaneous kind, which are rai-ely used and do not 

 fall under any of the above headings, such as the 

 trampling of many animals, a covey of partridges on 

 the wing, the roar of a waterfall or the rumbling of 

 waves in a cavern. 



To most observers and over the greater part of the 

 disturbed area, the soxmd remains of the same character 

 throughout. There is nearly always a very perceptible 

 change of intensity, the noise growing gradually louder 

 and then dying away, and the change sometimes takes 

 place so uniformly that it seems as if a carnage were 

 coming up rapidly to the door of the observer's house 

 and afterwards receding on the other side. Close to the 

 epicentre (or area vertically above the seismic focus), 

 a change in the character of the sound is also notice- 

 able at or about the instant when the shock is strongest ; 

 some hear a loud crash like the explosion of a bomb- 

 shell ; to others, it appears rougher and more grating ; 

 while a large number perceive no change at all. At 

 moderate distances, the changes are much less marked , 

 before and after the shock, the sound resembles the 

 moaning of the wind, and, while the shock lasts, a more 

 rumbling character is developed. At great distances, 

 the change in character is hardly sensible ; there is 

 little, if any, variation in intensity, and the report, when 

 heai'd, resembles more than anything else the deep 

 boom of distant thunder. 



The extraordinary depth of the sound is shown very 

 clearly by the descriptions given above. The frecjuent 

 and unprompted use of the word " heavy," whether 

 applied to thunder, explosions, or traction-engines, is 

 some evidence of this. The same impression is also con- 

 veyed by the more detailed accounts; "much lower 

 than the lowest thunder " one obsei-ver writes, and 

 another, " I can only compare the soiuid with the pedal 

 notes of a great organ, only of a deeper pitch than 

 can be taken in by the human ear, shall I sav a noise 

 more felt than heard?" Still more striking is the fact 

 that, while the sound is heard by some observers, it is 

 quite inaudible to others at the same place and even in 

 the same house. To one person the sound is so loud 

 that it seems like the rumbling of a heavy traction- 

 engine passing ; another in the same place and equally 

 on the alert will be just as positive that the shock was 

 unaccompanied by sound. The explanation offered 

 rather confidently by some writers that the attention 

 of the second observer was distracted by the shock is 

 untrCnable for several reasons, which may be worth men- 



tioning. (1) In the first place, the sound is often too 

 loud to escape notice in this way. (2) It is generally 

 heard before the shock begins to be felt. (3) Different 

 races, as will be seen afterwards, vary much in 

 their powers of hearing the earthquake-sound. A wholo 

 nation, and especially one so accustomed to observing 

 earthquakes as the Japanese, cannot be accused of con- 

 stant inatt«ntion. (4) Lastly, my own hearing is, I 

 believe, unusually keen for ordinary noises, but I could 

 hear no sound during the Hereford earthquake of 1896. 

 though I was in a quiet room and listened intently, 

 and more than 60 per cent, of the observers in Birming- 

 ham heard the earthquake-sound. We may therefore 

 conclude that the inaudibility of the sound is not due 

 to inattention, but simply to the fact that some observers 

 are deaf to very low sounds. 



Another fact deserving of notice is that the sound- 

 vibrations are not all of one pitch. The loud and deep 

 explosive crashes observable near the epicentre at the 

 time when the shock is strongest are only heard by 

 some persons. Again, the observers at any one place 

 make use of widely different means of comparison. 

 Thus, out of move than fifty observers of the Hereford 

 earthquake in Birmingham, 35 per cent, compared the 

 sound to passing waggons, etc., 18 per cent, to thunder, 

 17 to wind, 4 to loads of stones falling, 9 to the fall of 

 heavy bodies, 11 to explosions, and 6 per cent, to mis- 

 cellaneous sounds. The difference in loudness was also 

 very marked. On the one hand, we have such 

 descriptions as a traction-engine passing, an express train 

 rushing beneath an arch, a heavily laden cart passing 

 over a rough street, and heavy thunder ; on the other, 

 distant thunder, a rushing wind and a very distant ex- 

 plosion. If all the observers in one place wore equally 

 endowed, the sound would present the same character 

 to every one of them. But their powers differ widely. 

 Their ears, indeed, act like sieves of varying degrees of 

 fineness ; some are affected by many vibrations and 

 to them the sound is loud and complex ; others are im- 

 pervious to all but a few vibrations, and they hear a 

 sound that is apparently faint and monotonous. 



As the inhabitants of any one country do not agree 

 in this respect, it is only natural to suppose that '' dif- 

 ferent races should also varv. The people of Great 

 Britain seem to have unusually good powers of hearing 

 earthquake sounds. It may fairly be said that an 

 earthquake never occui's in t-hese islands without the 

 sound being heard. It is not altogether easy to make 

 a just comparison with other nations, for we cannot be 

 certain that the omission of sound-records is not acci- 

 dental. There are, however, two countries, Italy and 

 Japan, where earthquakes are closely studied. In Italy 

 about one-third, and in Japan about one-quarter, of the 

 earthquakes seem to be accompanied by sound. But 

 there is this difference between them. The Italian 

 shocks, which are unattended, so far as we know, by 

 sound, are generally felt by very few persons ; when 

 there are many obsen'ers, there are always one or more 

 to be found among them who are capable of hearing 

 deep sounds. But. in Japan, although the proportion 

 of audible earthcjuakes increases with the area shaken 

 by them, nearly one-third of the strongest shocks are 

 unaccompanied by an}' recorded sound. The only in- 

 ference we can make from this is that the Jajianese, as 

 a race, are less susceptible than Europeans to veiy low 

 sounds. 



The more or less limited size of the area over which 

 the sound is heard is also evidence of the less or greater 

 deafness of observers for low sounds. In Great Britain, 



