1907.1 AND CONTRACTION OF THE EARTH. 261 



up, and rivers forced out, sometimes even flame and hot springs, and at 

 others the course of rivers is turned. A terrible noise precedes and accom- 

 panies the shock; sometimes a murmuring, like the lowing of cattle, or like 

 human voices, or the clashing of arms. This depends on the substance 

 which receives the sound, and the shape of the caverns or crevices through 

 which it issues; it being more shrill from a narrow opening, more hoarse 

 from one that is curved, producing a loud reverberation from hard bodies, 

 a sound like a boiling fluid from moist substances, fluctuating in stagnant 

 water, and roaring when forced against solid bodies. There is, therefore, 

 often the sound without any motion. Nor is it a simple motion, but one 

 that is tremulous and vibratory. The cleft sometimes remains, displaying 

 what it has swallowed up ; sometimes concealing it, the mouth being closed 

 ' and the soil being brought over it, so that no vestige is left ; the city being, 

 as it were, devoured, and the tract of country engulfed. Maritime districts 

 are more especially subject to shocks. Nor are mountainous tracts exempt 

 from them ; I have found, by my inquiries, that the Alps and the Apennines 

 are frequently shaken. The shocks happen more frequently in the autumn and 

 in the spring, as is the case also with thunder. There are seldom shocks 

 in Gaul and in Egypt; in the latter it depends on the prevalence of summer, 

 in the former of winter. They also happen more frequently in the night 

 than in the day. The greatest shocks are in the morning and the evening; 

 but they often take place at daybreak, and sometimes at noon. They also 

 take place during the eclipses of the sun and of the moon, because at that 

 time storms are lulled. They are most frequent when great heat succeeds to 

 showers, or showers succeed to great heat. 



''Chap. 83 (81) — Signs of an Approaching Earthquake. 

 " There is no doubt that earthquakes are felt by persons on shipboard, 

 as they are struck by a sudden motion of the waves, without these being 

 raised by any gust of- wind. And things that are in the vessels shake as they 

 do in houses, and give notice by their creaking ; also the birds, when they settle 

 upon the vessels, are not without their alarms. There is also a sign in the 

 heavens ; for, when a shock is near at hand, either in the daytime or a little 

 after sunset, a cloud is stretched out in the clear sky, like a long thin line. 

 The water in wells is also more turbid than usual, and it emits a disagreeable 

 odour. 



"Chap. 84 (82) — Preservatives against Future Earthquakes. 

 " These same places, however, afford protection, and this is also the 

 case where there is a number of caverns, for they give vent to the con- 

 fined vapour, a circumstance which has been remarked in certain towns, 

 which have been less shaken where they have been excavated by many sewers. 

 And, in the same town, those parts that are excavated are safer than the 

 other parts, as is understood to be the case at Naples in Italy, the part of 

 which is solid being more liable to injury. Arched buildings are also the 

 most safe, also the angles of walls, the shocks counteracting each other; walls 

 made of brick also suffer less from the shocks. There is also a great dif- 

 ference in the nature of the motions, where various motions are experienced. 



