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This eBook from the Gutenberg Project consists of approximately 126 pages of information about Scientific American Supplement, No. 388, June 9, 1883.
is quite conceivable, and not incredible, that such a current may be gradually established and thenceforward permanently maintained by a small motor flame barely more than enough to overbalance the minimized friction.  This is not a supposed or theoretically inferred fact, like the facts of ventilation sometimes alleged by theorists.  On the contrary, the theory I have offered is merely an attempt to explain facts that I have witnessed and that anyone can verify with the anemometer.  But the theory by no means covers the art and mystery of ventilation; for ventilation is truly an art as well as a mystery.  The art lies in a consummate experience of the sizes, proportions, and forms of flues, their inlets, expansions, and exits, with many other incidental adaptations necessary, in order to insure under all circumstances the regular exhaustion of any specific volume of air required, per minute.  And this art has by one man been achieved.  It would be a double injustice if I should neglect from any motive to inform my audience to whom I am indebted for what I know about ventilation practically, and even for the knowledge that there is any such fact as a practicable ventilation of houses; one who is no theorist, but who has felt his way experimentally with his own hands, for a lifetime, to a practical mastery of the art to which I have attempted to fit a theory; every one present who is well informed on this subject must have anticipated already in mind the name of Henry A. Gouge.

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On the morning of the 20th of March, a long series of earthquakes spread alarm throughout all the cities and numerous villages that are scattered over the sides of Mt.  Etna.  The shocks followed each other at intervals of a few minutes; dull subterranean rumblings were heard; and a catastrophe was seen to be impending.  Toward evening the ground cracked at the lower part of the south side of the mountain, at the limit of the cultivated zone, and at four kilometers to the north of the village of Nicolosi.  There formed on the earth a large number of very wide fissures, through which escaped great volumes of steam and gases which enveloped the mountain in a thick haze; and toward night, a very bright red light, which, seen from Catania, seemed to come out in great waves from the foot of the mountain, announced the coming of the lava.

[Illustration:  ERUPTION OF MOUNT ETNA, MARCH 22, 1883.]

Eleven eruptions occurred during the night, and shot into the air fiery scoriae which, in a short time, formed three hillocks from forty to fifty meters in height.  The jet of scoriae was accompanied with strong detonations, and the oscillations of the ground were of such violence that the bells in the villages of Nicolosi and Pedara rang of themselves.  The general consternation was the greater in that the

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