I was not less than 4800 miles from the surface.
With this inference the indication of my barycrite substantially agreed.

The latter instrument consisted of a spring whose deflection by a given weight upon the equator had been very carefully tested.
Gravity diminishing as the square of the distance from the centre, it was obvious that at about 8000 miles--or 4000 above the Earth's surface--this spring would be deflected only one quarter as much by a given weight as on Earth: at 16,000 miles from the surface, or 20,000 from the centre, one-twenty-fifth as much, and so on.

I had graduated the scale accordingly, and it indicated at present a distance somewhat less than 9000 miles from the centre.

Having adjusted the helm and set the alarum to wake me in six hours, I lay down upon my bed.
The anxiety and peril of my position had disturbed me very little whilst I was actively engaged either in steering and manipulating my machinery, or in looking upon the marvellous and novel spectacles presented to my eyes; but it now oppressed me in my sleep, and caused me frequently to wake from dreams of a hideous character.

Two or three times, on such awaking, I went to examine the metacompass, and on one occasion found it necessary slightly to readjust the helm; the stars by which I steered having moved some second or two to the right of their proper position.
On rising, I completed the circuit which filled my vessel with brilliant light emitted from an electric lamp at the upper part of the stern, and reflected by the polished metallic walls.