Across the Zodiac, page 29 by Percy Greg
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ched it, to remain for some time above it. To do both, I must attain it, if possible, at the same moment at which I secured a westward impulse just sufficient to counterbalance the eastward impulse derived from the rotation of the Earth;--that is, in the latitude from which I started, a thousand miles an hour. I had calculated that while directing through the main bar a current of apergy sufficient to keep the Astronaut at a fixed elevation, I could easily spare for the eastward conductor sufficient force to create in the space of one hour the impulse required, but that in the course of that hour the gradually increasing apergic force would drive me 500 miles westward. Now in six hours the Earth's rotation would carry an object close to its surface through an angle of 90°; that is, from the sunset to the midnight meridian. But the greater the elevation of the object the wider its orbit round the Earth's centre, and the longer each degree; so that moving eastward only a thousand miles an hour, I should constantly lag behind a point on the Earth's surface, and should not reach the midnight meridian till somewhat later. I had, moreover, to lose 500 miles of the eastward drift during the last hour in which I should be subject to it, through the action of the apergic force above-mentioned. Now, an elevation of 330 miles would give the Astronaut an orbit on which 90° would represent 6500 miles. In seven hours I should be carried along that orbit 7000 miles eastward by the impulse my Astronaut had received from the Earth, and driven back 500 miles by the apergy; so that at 1 A.M. by my chronometer I should be exactly in the plane of the midnight meridian, or 6500 miles east of my starting-point in space, provided that I put the eastward apergic current in action exactly at 12 P.M. by the chronometer. At 1 A.M. also I should have generated a westward impulse of 1000 miles an hour. This, once created, would continue to exist though the force that created it were cut off, and would exactly counterbalance the opposi