rst," said Redgrave. "That was the
greatest of your father's discoveries. He got at the secret of
gravitation, and was able to analyse it into two separate forces just as
Volta did with electricity--positive and negative, or, to put it better,
attractive and repulsive.

"Three out of the five sets of engines in the _Astronef_ develop the R.
Force, as I call it for short. This wheel with the hundred degrees
marked behind it regulates the development. The further I turn it this
way to the right, the more the R. Force overcomes the attractive force
of the earth or any other planet that we may visit. Turn it back, and
gravitation asserts itself. If I put this arrow-head on the wheel
opposite zero the weight of the _Astronef_ is about a hundred and fifty
tons, and of course she would go down like a stone, and a very big one
at that. At ten she weighs nothing; that is to say the R. Force exactly
counteracts gravitation. At eleven she begins to rise. At a hundred she
would be hurled away from the earth like a shell from a twelve-inch gun,
or even faster. Now, watch."

He took up the speaking-tube. "Is she all tight everywhere, Andrew?"

"Yes, my Lord," came gurgling through the tube.

Then Redgrave slowly turned the wheel till the indicator pointed to
twenty-five. Zaidie, all eyes and wonder, saw a vast sea of glittering
white spread out beneath them, an ocean of snow with grey-blue patches
here and there. It sank away from under them till the patches became
spots and the sunlit clouds a vast, luminous blur. The air about them
grew marvellously clear and limpid. The sun blazed down on them with a
tenfold intensity of light, but Zaidie was astonished to find that very
little heat penetrated the glass walls and roof of the conning-tower.

"What an awful height!" she exclaimed, looking round at him with
something like fear in her eyes. "How high are we, Lenox?"

"You'll find afterwards that the _Astronef_ doesn't take any account of
high or low or up or down," he replied, looking at the dial of an
aneroid barometer by the side of him. "Roughly speaking, we're rather
over 60,000 feet--say ten miles--from the surface of the Atlantic.
That's why I asked Andrew whether everything was tight. You see we
couldn't breathe the air there is outside there--too thin and cold--and
so the _Astronef_ makes her own atmosphere as we go along. But I won't
spoil what you're going to see by any more of this. So if you please,
we'll go down now