more, to the plain below.

And one thing (aye! and I fear me, many) have I missed to set out with
particularness:

There was, as you do know, all around the base of the Pyramid, which was
five and one-quarter miles every way, a great circle of light, which was
set up by the Earth-Current, and burned within a transparent tube; or
had that appearance. And it bounded the Pyramid for a clear mile upon
every side, and burned for ever; and none of the monsters had power ever
to pass across, because of what we did call The Air Clog that it did
make, as an invisible Wall of Safety. And it did give out also a more
subtile vibration, that did affect the weak Brain-Elements of the
monsters and the Lower Men-Brutes. And some did hold that there went
from it a further vibration of a greater subtileness that gave a
protecting against the Evil Forces. And some quality it had truly
thiswise; for the Evil Powers had no ability to cause harm to any
within. Yet were there some dangers against which it might not avail;
but these had no cunning to bring harm to any _within_ the Great Redoubt
who had wisdom to meddle with no dreadfulness. And so were those last
millions guarded until the Earth-Current should be used to its end. And
this circle is that which I have called the Electric Circle; though with
failure to explain. But there it was called only, The Circle.

And thus have I, with great effort, made a little clear that grim land
of night, where, presently, my listening heard one calling across the
dark. And how that this grew upon me, I will set out forthwith.