*THE POPULAR SCIENCE MONTHLY.*

square, it will require 240 tons; if three inches square, it will scarcely break with 540 tons. Bars of steel are not often made larger than this, although Krupp, in his colossal works, doubtless makes some whose section equals 144 square inches. To pull apart such a bar would require a strain equal to the weight of 8,640 tons. It requires an effort to grasp the meaning of such a load. A stout team will haul two tons over a good road for a moderate distance; that number of tons would require more than 4,000 such teams to move it. If put upon a railroad it would need 864 cars and twenty-three locomotives to draw it. It would equal in weight one of the largest ocean-steamers with its complement of freight.

But we shall need a much larger unit than this. Could a bar of steel three feet square be forged—and, judging from the size of his steel cannon, Krupp might do this also—it would be able to lift nine times that great amount. Probably no furnace can much exceed this, but we may imagine a monster bar measuring one rod—1612 feet—square, and by easy multiplication we find its strength great enough to lift 3014 times as much as the last, or in figures 2,352,240 tons, three times the weight of the cotton crop of the United States when it equaled 4,000,000 bales.

To get a fit unit for our purpose we shall need to go far beyond this, but first pause to contemplate a bar of steel 16½ feet square. As it lay stretched upon the ground, we would need a ladder to get upon its upper side. Few rooms in private dwellings are 1612 feet high, and 1612 feet wide makes a spacious parlor.

Endeavor to get some idea of its tenacity, and how many million horses it would require to pull it asunder, and then, after getting somewhat accustomed to the greatness and strength of a bar of solid steel 1612 feet square, imagine one which is one mile square—5,280 feet wide, and as many thick. If it lay on the ground near the Catskill Mountains, its upper surface would overtop their highest summit by more than 1,000 feet. It would be equal to 102,400 such monster bars as the last. Its lifting power would be nearly 240,869,000,000 tons. The mind is utterly unable to grasp such figures. The whole globe contains 1,200,000,000 inhabitants. If each man, woman, and child, could pull with a force of 100 pounds—a large estimate—to move such a weight would require the united efforts of the inhabitants of two thousand such worlds as this.

As I shall have frequent occasion to speak of the load which such a bar could sustain, I shall, for convenience, call it in round numbers 240,000,000,000 tons, neglecting the other figures, because the number is so inconceivably great that taking from it a billion or so of tons will alter the result less than one half of one per cent. This bar is to be the unit of measure which I shall for the present employ, and with its help I shall attempt to give some idea of the influence of the sun in holding the system together, and of the attraction exerted by the