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THE WONDERS OF TERRESTRIAL DEPTHS
At eight in the morning a ray of daylight came to wake us up. Thethousand shining surfaces of lava on the walls received it on itspassage, and scattered it like a shower of sparks.
There was light enough to distinguish surrounding objects.
"Well, Axel, what do you say to it?" cried my uncle, rubbing hishands. "Did you ever spend a quieter night in our little house atKönigsberg? No noise of cart wheels, no cries of basket women, noboatmen shouting!"
"No doubt it is very quiet at the bottom of this well, but there issomething alarming in the quietness itself."
"Now come!" my uncle cried; "if you are frightened already, what willyou be by and by? We have not gone a single inch yet into the bowelsof the earth."
"What do you mean?"
"I mean that we have only reached the level of the island. longvertical tube, which terminates at the mouth of the crater, has itslower end only at the level of the sea."
"Are you sure of that?"
"Quite sure. Consult the barometer."
In fact, the mercury, which had risen in the instrument as fast as wedescended, had stopped at twenty-nine inches.
"You see," said the Professor, "we have now only the pressure of ouratmosphere, and I shall be glad when the aneroid takes the place ofthe barometer."
And in truth this instrument would become useless as soon as theweight of the atmosphere should exceed the pressure ascertained atthe level of the sea.
"But," I said, "is there not reason to fear that this ever-increasingpressure will become at last very painful to bear?"
"No; we shall descend at a slow rate, and our lungs will becomeinured to a denser atmosphere. Aeronauts find the want of air as theyrise to high elevations, but we shall perhaps have too much: of thetwo, this is what I should prefer. Don't let us lose a moment. Whereis the bundle we sent down before us?"
I then remembered that we had searched for it in vain the eveningbefore. My uncle questioned Hans, who, after having examinedattentively with the eye of a huntsman, replied:
And so it was. The bundle had been caught by a projection a hundredfeet above us. Immediately the Icelander climbed up like a cat, andin a few minutes the package was in our possession.
"Now," said my uncle, "let us breakfast; but we must lay in a goodstock, for we don't know how long we may have to go on."
The biscuit and extract of meat were washed down with a draught ofwater mingled with a little gin.
Breakfast over, my uncle drew from his pocket a small notebook,intended for scientific observations. He consulted his instruments,and recorded:
"Monday, July 1.
"Chronometer, 8.17 a.m.; barometer, 297 in.; thermometer, 6° (43°F.). Direction, E.S.E."
This last observation applied to the dark gallery, and was indicatedby the compass.
"Now, Axel," cried the Professor with enthusiasm, "now we are reallygoing into the interior of the earth. At this precise moment thejourney commences."
So saying, my uncle took in one hand Ruhmkorff's apparatus, which washanging from his neck; and with the other he formed an electriccommunication with the coil in the lantern, and a sufficiently brightlight dispersed the darkness of the passage.
Hans carried the other apparatus, which was also put into action.This ingenious application of electricity would enable us to go onfor a long time by creating an artificial light even in the midst ofthe most inflammable gases.
"Now, march!" cried my uncle.
Each shouldered his package. Hans drove before him the load of cordsand clothes; and, myself walking last, we entered the gallery.
At the moment of becoming engulfed in this dark gallery, I raised myhead, and saw for the last time through the length of that vast tubethe sky of Iceland, which I was never to behold again.
The lava, in the last eruption of 1229, had forced a passage throughthis tunnel. It still lined the walls with a thick and glisteningcoat. The electric light was here intensified a hundredfold byreflection.
The only difficulty in proceeding lay in not sliding too fast down anincline of about forty-five degrees; happily certain asperities and afew blisterings here and there formed steps, and we descended,letting our baggage slip before us from the end of a long rope.
But that which formed steps under our feet became stalactitesoverhead. The lava, which was porous in many places, had formed asurface covered with small rounded blisters; crystals of opaquequartz, set with limpid tears of glass, and hanging like clusteredchandeliers from the vaulted roof, seemed as it were to kindle andform a sudden illumination as we passed on our way. It seemed as ifthe genii of the depths were lighting up their palace to receivetheir terrestrial guests.
"It is magnificent!" I cried spontaneously. "My uncle, what a sight!Don't you admire those blending hues of lava, passing from reddishbrown to bright yellow by imperceptible shades? And these crystalsare just like globes of light."
"Ali, you think so, do you, Axel, my boy? Well, you will see greatersplendours than these, I hope. Now let us march: march!"
He had better have said slide, for we did nothing but drop down thesteep inclines. It was the facifs _descensus Averni_ of Virgil. Thecompass, which I consulted frequently, gave our direction assoutheast with inflexible steadiness. This lava stream deviatedneither to the right nor to the left.
Yet there was no sensible increase of temperature. This justifiedDavy's theory, and more than once I consulted the thermometer withsurprise. Two hours after our departure it only marked 10° (50°Fahr.), an increase of only 4°. This gave reason for believing thatour descent was more horizontal than vertical. As for the exact depthreached, it was very easy to ascertain that; the Professor measuredaccurately the angles of deviation and inclination on the road, buthe kept the results to himself.
About eight in the evening he signalled to stop. Hans sat down atonce. The lamps were hung upon a projection in the lava; we were in asort of cavern where there was plenty of air. Certain puffs of airreached us. What atmospheric disturbance was the cause of them? Icould not answer that question at the moment. Hunger and fatigue mademe incapable of reasoning. A descent of seven hours consecutively isnot made without considerable expenditure of strength. I wasexhausted. The order to 'halt' therefore gave me pleasure. Hans laidour provisions upon a block of lava, and we ate with a good appetite.But one thing troubled me, our supply of water was half consumed. Myuncle reckoned upon a fresh supply from subterranean sources, buthitherto we had met with none. I could not help drawing his attentionto this circumstance.
"Are you surprised at this want of springs?" he said.
"More than that, I am anxious about it; we have only water enough forfive days."
"Don't be uneasy, Axel, we shall find more than we want."
"When we have left this bed of lava behind us. How could springsbreak through such walls as these?"
"But perhaps this passage runs to a very great depth. It seems to methat we have made no great progress vertically."
"Why do you suppose that?"
"Because if we had gone deep into the crust of earth, we should haveencountered greater heat."
"According to your system," said my uncle. "But what does thethermometer say?"
"Hardly fifteen degrees (59° Fahr), nine degrees only since ourdeparture."
"Well, what is your conclusion?"
"This is my conclusion. According to exact observations, the increaseof temperature in the interior of the globe advances at the rate ofone degree (1 4/5° Fahr.) for every hundred feet. But certain localconditions may modify this rate. Thus at Yakoutsk in Siberia theincrease of a degree is ascertained to be reached every 36 feet. Thisdifference depends upon the heat-conducting power of the rocks.Moreover, in the neighbourhood of an extinct volcano, through gneiss,it has been observed that the increase of a degree is only attainedat every 125 feet. Let us therefore assume this last hypothesis asthe most suitable to our situation, and calculate."
"Well, do calculate, my boy."
"Nothing is easier," said I, putting down figures in my note book."Nine times a hundred and twenty-five feet gives a depth of elevenhundred and twenty-five feet."
"Very accurate indeed."
"By my observation we are at 10,000 feet below the level of the sea."
"Is that possible?"
"Yes, or figures are of no use."
The Professor's calculations were quite correct. We had alreadyattained a depth of six thousand feet beyond that hitherto reached bythe foot of man, such as the mines of Kitz Bahl in Tyrol, and thoseof Wuttembourg in Bohemia.
The temperature, which ought to have been 81° (178° Fahr.) wasscarcely 15° (59° Fahr.). Here was cause for reflection.
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