"Oh, I almost forgot to mention it." Arcot spoke slowly, dejectedly. "In the heat of the attack back there it went practically unnoticed. Our only weapon beside the gas is useless now. Do you remember how the ship seemed to lose its invisibility for an instant? I learned why when we investigated the ship. Those men are physicists of the highest order. We must realize the terrible forces, both physical and mental that we are to meet. They've solved the secret of our invisibility, and now they can neutralize it. They began using it a bit too late this time, but they had located the radio-produced interference caused by the ship's invisibility apparatus, and they were sending a beam of interfering radio energy at us. We are invisible only by reason of the vibration of the molecules in response to the radio impressed oscillations. The molecules vibrate in tune, at terrific frequency, and the light can pass perfectly. What will happen, however, if someone locates the source of the radio waves? It'll be simple for them to send out a radio beam and touch our invisible ship with it. The two radio waves impressed on us now will be out of step and the interference will instantly make us visible. We can no longer attack them with our atomic hydrogen blast, or with the gas--both are useless unless we can get close to them, and we can't come within ten miles of them now. Those bombs of theirs are effective at that distance." Again he fell silent, thinking--hoping for an idea that would once more give them a chance to combat the Kaxorians. His three companions, equally depressed and without a workable idea, remained silent. Abruptly Arcot stood up. "I'm going to speak with the Commander-in-Field here. Then we can start back for Sonor--and maybe we had better head for home. It looks as though there is little we can do here." Briefly he spoke to the young Venerian officer, and told him what he had learned about the ship. Perhaps they could fly it to Sonor; or it could be left there undestroyed if he would open a certain control just before he left. Arcot showed him which one--it would drain out the power of the great storage tank, throwing it harmlessly against the clouds above. The Kaxorians might destroy the machine if they wanted to--Arcot felt that they would not wish to. They would hope, with reason, they might recapture it! It would be impossible to move that tremendous machine without the power that its "tank" was intended to hold. VII