mineral beds of virgin oxides, set up a tremendous chemical action, whose resultant heat accounted for all the phenomena. There was much to be said for this theory, the volcanic explosions being clearly due to water in the form of superheated steam and compressed gases. The objections were greater still, however, as they were also to the intermediate theory of a solid core, a solid crust, and a layer of molten matter between.

It was and is known, however, that the interior of the earth is in a state of tremendous heat. This is shown by the rising of the thermometer one degree for about every sixty feet of depth as we descend into mines and wells. This rising of the thermometer is, however, not regular in any one place, but very irregular in all places. The Comstock Lode, for instance, increases in heat much more rapidly than the deep well at Budapest; and in the latter, after a great depth has been reached, the thermometer begins. to fall. The seismograph, or earthquake recorder, has furnished the most satisfactory suggestion yet obtained. By a series of observations at stations widely separated, the area of various earthquakes has been measured and mapped. This has revealed the center, or starting-point, of the

satisfactory answer on these points seems to be impossible.

It was a cherished conviction of the schoolbooks some years ago that our earth was a molten mass in its interior, with a cooled crust outside upon which we dwell. This idea, however, the astronomers and mathematicians long since showed to be erroneous, and it has been abandoned. Our earth is solid and rigid to its core. Otherwise the tremendous tension exerted by the forces of gravity which play upon it would distort it into varying shapes at varying periods. Lord Kelvin showed many years ago, by undeniable mathematics, that if the earth had a molten interior, as was supposed, with a crust of solid steel 500 miles in thickness, the forces of gravity would at times pull it out of the spherical form and contort it as a boy squeezes a soft rubber ball. The molten interior as the source of volcanic action then gave place to the chemical theory. This was the conception that air and water from the surface, percolating downward and coming into contact with

curately predicted in point of time. Vesuvius, it appears, is as untamable and uncertain as ever.

"On

gations have induced the present belief that the causes of volcanic action are not due to a reservoir of molten rock in the earth's interior, but to local causes operating, in the case of any given volcano or group, over a limited area and at no great distance, comparatively speaking, below the surface.

This is the view taken by Professor Semmola, who, since the death of Professor Palmieri last year, has occupied the position of Director of the Observatory of Vesuvius. He is also Professor of Meteorology in the University of Naples, and is credited with a large number of original investigations in this and allied sciences. Professor Semmola is a tall, distinguished-looking man, whose appearance is German rather than Italian. A request for information as to what we do not know about volcanoes brings an invitation to his rooms in the University. He begins the conversation by saying that two reports have gone the rounds of the European press for which there was no foundation. The first was that Vesuvius was in the last throes, and no more eruptions were to be expected. The second was that science had reached a point of exactness by which future eruptions could be ac

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'That depends upon the character of the eruption; but eruptions vary greatly. fact, no two are alike. In a normal or ordinary eruption, the bed of the crater slowly rises. It rose steadily, for instance, from 1875 to 1878, and the lava then overtopping the brim, flowed down the side of the cone. In eccentric eruptions, the action sets up suddenly and violently, and breaks open new craters or blows out the cold lava that fills the old channels. The heat of the issuing lava varies also. It is usually about 1,800 degrees Fahrenheit, but may be much hotter. It remains fluid down to about 1,200 degrees." "What is the latest theory of volcanic action?"

"We are still working at the old theories, the electro-chemical and that of a reservoir of molten matter below. The lack of knowl

edge as to the active cause arises from the impossibility of studying the action at its source. Nobody," said he, smiling, "wants to go down into the crater of an active volcano, and his investigations would not reach the publisher if he did.

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"We know, however," he continued, that the interior of the earth still conserves a high degree of heat. Taking the varying rate of augmentation of temperature in descending mines and wells, a distance of twenty or thirty miles would give us a heat capable of melting all known matter. The matter forming the earth at this depth is solid through pressure. If the pressure were removed it would at once liquefy, and forced out through a volcano it does liquefy. I am aware that there are objections to be urged against this theory as accounting for all volcanic phenomena, but I give it to you as perhaps the most reasonable basis of a theory that can be presented."

The belief prevailed for some time that the periods of greatest activity of Vesuvius were coincident with those of the moon's greatest attraction. I investigated this question very thoroughly both by observations for two years and an extended comparison of past records of the moon and the volcano. It became fully evident that no variations whatever in activity were to be attributed to the moon's phases. Were there a molten interior, this, of course, could not be so."

"What mechanical power seems to be responsible for the tremendous force of the eruptions?"

"Steam, superheated, under great pressure. Given matter at a high degree of heat, and water which by some means reaches it, and you have a sufficient physical force to account for all the work done. That water plays a very important part in the eruptions is clearly evident. In some eruptions of Vesuvius an enormous amount of water has

"No. Even without the unanswerable objections of astronomy and mathematics, the idea is not tenable; other facts disprove it.

the sea, and of the wells and springs in the surrounding country, established an obvious relation. Many unofficial records of past eruptions describe the sinking of the sea,

fish stranded on the shores thus laid bare, etc. Palmieri, however, came to the conclusion, based on his investigation of the eruption of 1861, that it was not the sea that sank, but the coast that lifted. He found that, in the eruption, the coast was lifted for several miles, the highest elevation being at Torre del Greco, where the elevation was four feet and a half. It slowly sank to its former level, but two years afterwards had not quite attained it.

"This explosive and eruptive action of water is shown," he added, "whenever a lava flood passes over a spring. A miniature volcano forms and spouts. The water turns to steam, and this, superheated and confined, bears the superincumbent weight only as long as it is unable to lift it. When the amount and power of the steam is equal to the demand, it erupts with violence through the lava flood and gives us a small volcano. After an eruption of Vesuvius, the lava which has cooled fills all the canals and vents leading from below. The steam and other gases which form below are thus unable to escape, and may go on augmenting in force for a long period. When the force of expansion attains the bursting point, it either blows out the old vents or forces new ones, sometimes in the volcano, and sometimes elsewhere, as when the new volcano of Monte Nuovo appeared above Pozzuoli in 1538. The so-called smoke from Vesuvius is almost entirely steam. Steam is absorbed by the lava before eruption, under great pressure, and is given off for long periods, as has been the case with the lava stream on the mountain for many months past."

"How deep, then, do you think the center of activity of Vesuvius lies?"

"I can only give you my opinion, and an opinion does not call for a demonstration. I think it is a matter of miles, perhaps ten, but probably less."

The mystery of the volcano remains still, therefore, the mystery of the earth itself; and we shall understand the one only when we understand the other. But the enormous heat and force of Vesuvius, only utilized thus far in supplying building stone and destroying buildings, recall practically the prophecy of Professor Berthelot, that in the golden age that is coming we shall draw all our heat, and the mechanical forces which result from its conversion, directly from the earth itself that instead of digging 2,000 feet for coal, we shall dig a little farther when the coal gives out, and bring up the heat itself by thermo-electric methods.