I
had to reach this line, and having reached 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 deg.; 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.
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