Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/440

Rh sense of heat at the moment, so pointedly referred to by Signor D'Errico, does not seem to have been felt elsewhere, so far as my inquiries enable me to judge.

Such oppressive glows have often preluded tornadoes, as in the great cyclone of the British Isles of 1839, when it was felt strongly in the east of Ireland; in this case, there is a traceable connection with the main disturbance; it is difficult to see any as direct with earthquake; but if intense local subterraneous pressure can disturb electrical equilibrium and produce earth light, it is not improbable that it may also and more directly produce earth heat.

The tables of the Meteorological Marine Observatory at Naples, which I have given, Part II., prove, that there was disturbance in the amount of rain for a period of several months anterior, as compared with former years; but there was no particular disturbance of rain, of the barometer, or of the magnetometer at the moment, or rather at the times of observation, on the same day. If there really was an emanation of earth light, from about the focal region at the time of the shock, analogy with the aurora might induce us to presume that there would also be some disturbance of the magnetometer; such disturbance might not, however, be sufficient to have been observable at Naples, in any case, as that city is at least sixty miles from the circumference of the region within which the earth light was said to have been developed.

Humboldt found that the magnetic needle was not disturbed in any South American shock in which he attended to it. His instruments, however, were not of the delicacy since employed; and it does not follow that, because the results were negative at his stations, disturbance might not