“Wade, how is it that those ships can be invisible when they are driven by light, and have the light stored in them? They're perfectly transparent. Why can't we see the light?”
“They are storing the light. It's bound—it can't escape. You can't see light unless it literally hits you in the eye. Their stored light can't reach you, for it is held by its own attraction and by the special field of the big generators.”
They seemed to be above one of the Kaxorian planes now. Arcot caught the roar of the invisible propellers.
“To the left, Wade—faster—hold it—left—ah!” Arcot pushed a button.
Down from the Solarite there dropped a little canister, one of the bombs that Arcot had prepared the night before. To hit an invisible target is ordinarily difficult, but when that target is far larger than the proverbial side of a barn, it is not very difficult, at that. But now Arcot's companions watched for the crash of the explosion, the flash of light. What sort of bomb was it that Arcot hoped would penetrate that tremendous armor?
Suddenly they saw a great spot of light, a spot that spread with startling rapidity, a patch of light that ran, and moved. It flew through the air at terrific speed. It was a pallid light, green and wan and ghostly, that seemed to flow and ebb.
For an instant Morey and the others stared in utter surprise. Then suddenly Morey burst out laughing.
“Ho—you win, Arcot. That was one they didn't think of, I'll bet! Luminous paint—and by the hundred gallon! Radium paint, I suppose, and no man has ever found how to stop the glow of radium. That plane sticks out like a sore thumb!”
Indeed, the great luminous splotch made the gigantic plane clearly evident against the gray clouds. Visible or not, that plane was marked.
Quickly Arcot tried to maneuver the Solarite over another of the great ships, for now the danger was only from those he could not see. Suddenly he had an idea.