a matter of fact, the thing, while difficult perhaps to understand in
principle, in operation works very simply. Miela knew that, and merely
asked them to show her how to operate it practically. This they did. She
spent two days with them--she learns things rather easily, you know--and
then she was ready."

I waited in amazement.

"For practical purposes all she had to understand was the operation of
these keys. The pressure of the light-ray in these coils"--he was standing
beside a row of wire coils which in the semidarkness I had not noticed
before--"is controlled by the key-switches." He indicated the latter as he
spoke. "They send a current to the outer metal plates of the car which
makes them repel or attract other masses of matter, as desired.

"All that Miela had to understand then was how to operate these keys so as
to keep the base of the vehicle headed toward the earth. They took her to
the outer edge of the atmosphere of Mercury over the Dark Country and
showed her the earth. They have used terrestrial telescopes for
generations, and since the invention of this vehicle telescopes for
celestial observation have been greatly improved.

"All Miela had to do was keep the air in here purified. That is a simple
chemical operation. By using this attractive and repellent force she
allowed the earth's gravity and the repelling power of the sun and Mercury
to drive her here."

He paused.

"But, doesn't she--don't you understand the thing in detail?" I asked
finally.

"I think father and I understand it now better than she does," he
answered. "We have studied it out here and questioned her as closely as
possible. We understand its workings pretty thoroughly. But the exact
nature of the light-ray we do not understand, any more than we understand
electricity. Nor do we understand this metallic substance which when
charged with the current becomes attractive or repellent in varying
degrees."

"Yes," I said. "That I can appreciate."

"Father has a theory about the light-ray," he went on, "which seems rather
reasonable from what we can gather from Miela. The thing seems more like
electricity than anything else, and father thinks now that it is generated
by dynamos on Mercury, similar to those we use here for electricity."

"Along that line," I said, "can you explain why this light-ray, which will
immediately set anything on fire that is combustible, and which acts
through metal, like those artillery shells, for i