[12] In all accounts of great eruptions of Mount Etna and Mount Vesuvius, I have found mention of this sort of lightning. Pliny the younger, in his second letter to Tacitus upon the eruption of Vesuvius in the time of Titus, says, that a black and horrible cloud covered them at Misenum (which is above fifteen miles from the Volcano), and that flashes of zig-zag fire, like lightning, but stronger, burst from it; these are his words: "ab altero latere nubes atra et horrenda ignei spiritus tortis vibratisque discursibus rupta, in longas flammarum figuras dehiscebat; fulgoribus illae et similes et majores erant." This was evidently the same electrical fire, and with which I am convinced that the smoak of all Volcanos is pregnant. In several accounts of the great eruption of Vesuvius in 1631, mention is made of damage done by the lightning that issued from the column of smoak. Bulifon, in particular, says, that, in the neighbourhood of the Volcano, people were struck dead in the same manner as if by lightning, without having their cloaths singed. Pliny mentions a like instance, which shews that the ancients had observed this phaenomenon; for he says, that at Pompeii, the day being fair, Marcus Herennius was struck dead by lightning. These are his words; "In Catilianis prodigiis, Pompeiano ex municipio M. Herennius Decurio _serena die_, fulmine ictus est." Plin. Hist. Nat. lib. II. cap. LI. The learned and ingenious Father Beccaria, at Turin, assured me, that he had been greatly pleased with my observations on this species of lightning, as coinciding perfectly with several of his electrical experiments. [13] "I am well convinced, by this collection, that many variegated marbles, and many precious stones, are the produce of Volcanos; and that there have been Volcanos in many parts of the world, where at present there are no traces of them visible." This is taken from a prior letter to Lord Morton, dated April 7, 1767. [14] In some accounts of an eruption of Vesuvius in 1660, I find mention made of ashes which fell in the shape of crosses, and were looked upon as highly miraculous; but in one book upon this subject, intituled, _Athanasii Kircheri Soc. Jes. De prodigiosis crucibus, &c. Romae_, MDCLXI, a very philosophical account is given of this phaenomenon; he says, that, in 1660, from the 16th of August to the 15th of October, Vesuvius cast up ashes, impregnated with nitrous, saline, and bituminous sulphur, which upon linen garments took the form of crosses, probably directed by the cross-threads in the linen, and therefore that the salts did not shoot into such a shape when they fell upon garments of woollen; a very particular description of these crosses may be found in page 38, of the abovementioned book.