Finally they reached another archipelago a few hundred miles in extent,the larger islands of which were covered with a sheet of ice,at the edges of which small icebergs were being formed by breaking off and slowly floating.Finding a small island on which the coating was thin,they grounded the Callisto,and stepped out for the first time in several days.The air was so still that a small piece of paper released at a height of six feet sank slowly and went as straight as the string of a plumb-line.The sun was bisected by the line of the horizon,and appeared to be moving about them in a circle,with only its upper half visible.As Jupiter's northern hemisphere was passing through its autumnal equinox,they concluded they had landed exactly at the pole.
"Now to work on our experiment,"said Cortlandt."I wonder how we may best get below the frozen surface?""We can explode a small quantity of dynamite,"replied Bearwarden,"after which the digging will be comparatively easy."While Cortlandt and Bearwarden prepared the mine,Ayrault brought out a pickaxe,two shovels,and the battery and wires with which to ignite the explosive.They made their preparations within one hundred feet of the Callisto,or much nearer than an equivalent amount of gunpowder could have been discharged.
"This recalls an old laboratory experiment,or rather lecture,"said Cortlandt,as they completed the arrangements,"for the illustration is not as a rule carried out.Explode two pounds of powder on an iron safe in a room with the windows closed,and the windows will be blown out,while the safe remains uninjured.
Explode an equivalent amount of dynamite on top of the safe,and it will be destroyed,while the glass panes are not even cracked.
This illustrates the difference in rapidity with which the explosions take place.To the intensely rapid action of dynamite the air affords as much resistance as a solid substance,while the explosion of the powder is so slow that the air has time to move away;hence the destruction of the windows in the first case,and the safe in the second."When they had moved beyond the danger line,Bearwarden,as the party's practising engineer,pressed the button,and the explosion did the rest.They found that the ground was frozen to a depth of but little more than a foot,below which it became perceptibly warm.Plying their shovels vigorously,they had soon dug the hole so deep that its edges were above their heads.When the floor was ten feet below the surrounding level the thermometer registered sixty.
"This is scarcely a fair test,"said Cortlandt,"since the heat rises and is lost as fast as given off.Let us therefore close the opening and see in what time it will melt a number of cubic feet of ice."Accordingly they climbed out,threw in about a cart-load of ice,and covered the opening with two of the Callisto's thick rugs.
In half an hour all the ice had melted,and in another half hour the water was hot.
"No arctic expedition need freeze to death here,"said Bearwarden,"since all a man would have to do would be to burrow a few feet to be as warm as toast."As the island on which they had landed was at one side of the archipelago,but was itself at the exact pole,it followed that the centre of the archipelago was not the part farthest north.
This in a measure accounted for the slight thickness of ice and snow,for the isobaric lines would slope,and consequently what wind there was would flow towards the interior of the archipelago,whose surface was colder than the surrounding ocean.
The moist air,however,coming almost entirely from the south,would lose most of its moisture by condensation in passing over the ice-laden land,and so,like the clouds over the region east of the Andes,would have but little left to let fall on this extreme northern part.The blanketing effect of a great thickness of snow would also cause,the lower strata of ice to melt,by keeping in the heat constantly given off by the warm planet.
