Virginia said nothing. She nodded sagely, and her nod was based upon the fact that she knew he was right but could not say so lest she be forced to tell the rest of her story.
"So," he said, "we can assume that something was either generated or present in the mixture at Alamogordo that, in one case, stopped the reaction, in the next case, permitted the thing to work and, in the third case, started the atomic fire in the earth."
"How do you go about finding it?" she asked. Virginia was interested. This theory was new to her, but it sounded reasonably solid.
He grinned unhappily. "The trouble with making experiments in atomic explosions is that it leaves so little stuff to measure afterwards." He lifted a crystal of the space-resonant elements and looked at it with wrinkled forehead.
"Something in this crystal holds the answer. I think we should analyze this material right down to the most infinitesimal trace. Then we can find out which of the included elements is responsible for the original problem."
"I can help," said Virginia.
He smiled grimly. "Your job is to keep an eye on Maddox and Kingston. See if you can locate their men on Earth One, also see what you can do toward locating those four subcritical masses. We must keep Kingston and the rest of his gang from entering Earth One." He looked at her thoughtfully. "Also keep an eye on your own collection."
Virginia smiled and nodded. She looked him squarely in the eye and said, "My collection of those elements is very small."
"Um," he said. "It's more than possible that the various functions of the space-resonant elements depends upon their mass. For instance, a small quantity might be suitable for mere communication—a larger quantity may be required for the visual communication, while a still larger mass is needed for a physical transfer.
"How their division comes with respect to the transfer of objects or messages from time plane to time plane is something that might be baffling."