Smohe-Rings of Vesuvius. 327 



few minutes, and it now appeared, npon watching the action, 

 that occasionally the subterranean explosion and slight tremor 

 which invariably preceded the jet of molten matter were 

 deadened, and, as it were, muffled. When this was the case, 

 they were followed, not as nsual, by a shower of stones, but by 

 a huge globe of smoke, which, hurled upwards to a height of 

 several hundred feet, there exploded, and became a true smoke- 

 ring ; the contained gas in its escape producing the wild scream 

 which I have mentioned, and the effect of which in the utter 

 stillness and solitude of a summer noon was somewhat startlino-. 

 We soon found that a little practice enabled us to discriminate 

 with perfect certainty between the eructations which preceded 

 a discharge of lapilli, and those which announced another 

 smoke-ring, and came to the following rough theory as to the 

 volcanic action. It would seem that the gas when generated 

 in Nature's laboratory becomes enveloped in a coating or case of 

 vapour. If this coating be of sufficient density to resist the elastic 

 force of the gas till it reach the external air, a smoke-globe and 

 ring are produced ; if, on the contrary, the disruption of the 

 envelope take place within the volcano, the gas encountering 

 the mass of light stones which are continually dancing within the 

 throat of the motmtain like a pith or glass ball on a fountain-jet, 

 hurls them upward in its effort to escape. The simile of a pith- 

 ball will appear bold even to ridicule when it is remembered 

 that the projected masses are sometimes, though bat rarely, 

 larger than an ordinary house. These, however, are so excep- 

 tional, that no one would venture to theorize as to the position 

 they may have occupied previous to their ejection from the fiery 

 gulf; the ordinary lapilli, varying in size from a hazel-nut to a 

 cocoa-nut or football, may, under favourable circumstances, be 

 actually seen dancing in a thick crust a few feet below the 

 mouth of the volcano. The inward rotary motion of the various 

 parts of the ring as described by your correspondent was very 

 discernible in these colossal specimens, and may, I think, be 

 thus accounted for. The smoke-globe is first torn asunder in 

 its upper portion by the ascending gas, the lower portion is 

 then rent by the influx of atmospheric air, and this current will, 

 in the act of forming the ring, give to its component particles 

 the spinning motion, not inaptly compared by M. Tegetmeier 

 to a ring of buttons rotating on their axes. What atmospheric 

 conditions may be most suitable to the production of smoke- 

 rings I cannot say ; but I never saw them except in very calm 

 weather, usually, as above-mentioned, before sunrise ; and on 

 the last-described occasion, though it was past mid-day, the 

 usual sea-breeze had failed, and the air was hot and stagnant. 



Habeow, October 28tb } 1863. 



