Mr. Editor,
The following concise account of the appearances preceding and attending earthquakes generally, extracted from Dr. Wittich, may [have?] been read by many of your subscribers, [to?] others it may be acceptable. The efficient [cause?] of earthquakes mentioned by the Dr., although it is frequently so, is not the only one. If you deem this worth publishing, I [shall not regret] copying it, and will, if you wish, send you some other opinions of experienced philosophers, as to the proximate cause, effects, and [damages?] of earthquakes generally.
'Earthquake is a violent & sudden concussion of the earth, which is generally attended with uncommon noise, both in the air and under land; in consequence of which whole cities have been at once leveled, as [well] as [lands?]; the course of rivers altered, and the [most?] dreadful devastation have been occasioned. - - There is no phenomenon in nature more [calculated?] to impress the human mind with fear, than an earthquake, but it has not fully been investigated with philosophical [precision?], and the history of these events still remain very incomplete - - of the observations which indefatigable naturalists have been able to [collect?]: the following are the principal - - 1. [unreadable] there are any volcanoes, or burning [mountains?], earthquakes may naturally be [expected] to occur more frequently than in other [areas?]. 2. Earthquakes are in general preceded by long droughts; but they do not [always?] happen immediately after them. 3. They [unreadable] frequently indicated by certain [ethereal?] appearances in the atmosphere, [namely] the Aurora-Borealis, the falling stars & etc. [4. unreadable] short time previous to the shock the sea [sounds?] with a loud noise, fountains are disturbed and become muddy; and the irrational minds appear frightened, as if conscious of pending calamity. 5. The air at the time [unreadable] before the shock is in general very calm and [serene?] and afterwards becomes dark and [cloudy. 6.?] The concussion (or undulatary vibration) [comes?] with a rumbling noise, similar to that of [unreadable]; a rushing sound resembling wind [is sometimes?] heard; at others explosions, not [dissimilar to?] the firing of cannon, and the ground is [moved in?] differing directions, a single shock [may exceed?] a minute in its duration; but frequent concussions succeed each other at short intervals for a considerable length of time. 7. During the shock chasms are perceptible, and though the Abysses formed in the earth are in general not extensive, yet in violent earthquakes, they have been so large, as to bury whole cities. 8. The water of the ocean is on such occasions, affected still more than the land, the sea now rising to a considerable height, now dividing to a considerable depth, & emitting great quantities of air flames and smoke. Lastly the effects of earthquakes are not confined to one particular district or country, and frequently [extend?] to very distant regions; though there is no instance of the whole Globe having been convulsed at the same time.
The Cause of earthquakes or the theory of this tremendous phenomenon is but imperfectly understood, (among other causes,) it is however certain, they arise from the confinement of air within the bowels of the earth, where it is generated by sulphuric vapours, acting on different metalic ores, the principal, and most copious of which, appears to be iron. In confirmation of which theory we shall only observe that artificial earthquakes may be easily produced, by burying equal quantities of iron filings and sulphur mixed in a moist state, and confined in a vessel, so as to exclude the access of external air, and prevent the escape of the inflamable gas thus generated. In a few days (and if large quantitites be employed, in a few hours,) this composition grows remarkable hot, and will explode with a violence and impetuosity resembling the natural phenomenon: but we do not advice our junior readers to attempt such dangerous experiments - - an ample account of the latest and most awful earthquakes which have happened in the memory of man may be found by the inquisitive, in 73 vol. Philosophical Transactions of the Royal Society for 1783.
