counts for that superficial movement of the earth, that universal instantaneous shock, which made every house in London to tremble, none to fall: That quivering, tremulous, horizontal vibration, highly different from any motion we must conceive, to be produced from subterraneous evaporations. Hence authors tell us, Dec. 30, 1739, describing an earthquake in the west-riding of Yorkshire: It seem'd as if the earth mov'd backward and forward horizontally; a quivering, with reciprocal vibrations.
Mr. Flamsted rightly accounts the motion of earthquakes to be undulatory; and by being continued, causes a like motion to a great distance. As when you strike a long stretch'd string of wire at one end, the motion is immediately continued to the other. So far he entered into the nature of electricity.
Tho' he be in the right, thinking the cause comes from the air, yet what follows, contradicts his own hypothesis. For if a calm be necessary before an earthquake; then 'tis not produced by any turbulence in the air. Nor can we imagine that any aerial commotion, tho' it may shake windows, chimneys, and the like, shall reach 500 miles distance, split the solid earth, destroy whole cities, and cause those dire desolations we hear of.
