Natural Questions Chapter 12

Spiritum esse qui moueat et plurimis et maximis auctoribus placet. Archelaus, uir quidem satis diligens, ait ita: Uenti in concaua terrarum deferuntur; deinde, ubi iam omnia spatia plena sunt et in quantum aer potuit densatus est, is qui superuertit spiritus priorem premit et elidit ac frequentibus plagis primo cogit, deinde proturbat; tunc ille quaerens locum omnes angustias dimouet et claustra sua conatur effringere: sic euenit ut terrae, spiritu luctante et fugam quaerente, moueantur. Itaque cum terrae motus futurus est, praecedit aeris tranquillitas et quies, uidelicet quia uis spiritus, quae concitare uentos solet, in inferna sede retinetur. Nunc quoque, cum hic motus in Campania fuit, quamuis hiberno tempore et inquieto, per superiores dies caelo aer stetit. Quid ergo? Numquam flante uento terra concussa est? Admodum raro; duo si simul flauere uenti fieri; tamen et potest et solet. Quod si recipimus et constat duos uentos rem simul gerere, quidni accidere possit ut alter superiorem aera agitet, alter infernum?

Mais l’air est le mobile qu’admettent les plus nombreuses et les plus grandes autorités. Archelaüs, très-versé dans l’antiquité, s’exprime ainsi : « Les vents s’engouffrent dans les cavités de la terre ; là, quand tout l’espace est rempli, et l’air aussi condensé qu’il peut l’être, le nouvel air qui survient foule et comprime le premier, et de ses coups redoublés il le resserre, puis le disperse en désordre. Celui-ci, qui cherche à se faire place, écarte tous les obstacles et s’efforce de briser ses barrières ; ainsi arrivent les tremblements de terre, par la lutte de l’air impatient de fuir. Ces commotions ont pour avant-coureur un air calme et que rien n’agite, parce que la force impulsive, qui d’ordinaire déchaîne les vents, est concentrée dans les cavités souterraines. » Naguère, en effet, lors du tremblement de la Campanie, bien qu’on fût en hiver, l’atmosphère quelques jours avant fut constamment tranquille. Qu’est-ce à dire ? La terre n’a-t-elle jamais tremblé un jour de vent ? Il est bien rare que deux vents soufflent à la fois. La chose pourtant est possible et se voit : si nous admettons, et s’il est constant que deux vents opèrent simultanément quand le sol tremble, pourquoi l’un n’agiterait-il pas l’air supérieur, l’autre l’air souterrain ?

Many of the greatest authorities are persuaded that earthquakes are to be attributed to air. Archelaus, who is well versed in the records of antiquity, speaks thus: Winds are carried down into the earth’s hollows and recesses. When they are all full, and the atmosphere is condensed to the utmost extent, the air, which continues to come in, forces and thrusts the former air, and with frequent blows first compresses and then dislodges it. The air in its endeavour to find room forces all the narrow passages and tries to burst its barriers. Through the struggle of the air as it seeks for an escape it comes to pass that the earth is moved. This explains why the approach of an earthquake is preceded by still and quiet of the atmosphere; the force of the air which is wont to rouse the winds is held in check in its nether abode. Even on the present occasion of the earthquake in Campania, although the season was winter, the atmosphere was perfectly still and calm for several days before it. Well, then, did an earthquake never take place when there was a wind blowing? On very rare occasions have there been two winds blowing simultaneously. Still, such a thing is possible, and is wont to occur. But if we admit it as an established fact that two winds can be in activity at one and the same time, why shouldn’t it happen that [at times] one of them agitates the upper air, the other the nether? The text is uncertain, and the argument down to the end of the chapter rather obscure. The argument seems to be: Two winds can blow simultaneously. One may be beneath the earth (causing or during earthquake), one above. Therefore, stillness of the upper atmosphere is not a necessary concomitant of earthquake. The fact has at times been otherwise.