"I told you," he began without preamble, "that I had a vague theory about those spheres. Well, I know now. Randall proved it this afternoon. There can be no doubt that those globes are radio-active--the way they react to our atom-guns leads me to believe that they subsist on energy--radiant energy from the mineral and radio-actives of this planetoid. Their atomic scale must be such that their component atoms make up the two missing elements in our atomic scale! _This is the first time that man has ever encountered these two elements._ And of course, this is the first time these spheres have ever encountered humans--organic life--on an atomic scale so far removed from their own. Naturally they're curious. They tried to investigate and what they encountered from Randall was _fear_! _Perhaps the second strongest emotion._ Our fear must send out intangible vibrations that impinge harshly upon their own vibrations and lead them to attack. What fear arouses in them, we shall probably never know. The fact is that our human emotion of _fear_ in conflict with their vibratory rate renders them fatal, and even seems to draw them with a strange magnetic attraction!" For a moment every one of the four was silent, as the explanation cleared so much of the mystery before them. Then Captain Dennis walked over to the locker where the space-suits were racked. He began slipping into one of the bulky suits. "I'm going outside again. If this spacer's insulation against the spheres, there's no reason why a space-suit should not be also. Two of you cover me from the stern turret, and two--including a crew member, from the forward turret, you can at least delay their attack by blasting air currents, in case _they do attack_!" He dogged the last clamp into place and moved heavily through the doorway. * * * * * The men watching from the gun turrets saw Dennis approach the vast pit which seemed to be the abode of the sphere. The face-plate of his helmet was open. For minutes he stood motionless on the rim of the pit. They knew he was concentrating, duplicating the emotion of fear. Then with a catch in their throats they observed groups of the spheres rise majestically from the depths and swoop toward the waiting Dennis. With a swift gesture Captain Brooke snapped the face-plate closed. The spheres came to a complete stop about twenty feet from the waiting captain. The globes pulsed gently, as if waiting ... waiting. Again Dennis opened the face-plate wide, then snapped it shut. In the brief interval the spheres had darted into action, sweeping closer. Turning at last, Captain Dennis strode back to the ship, and slowly the flaming globes sank back into the pit out of sight. "It works," Scotty yelled delightedly, as the other men ran to their airlock to greet their Captain.