"I've seen that until I dream of it. It's one Phyfe tried to make the most of in his frequency determinations. It looks like nothing more than some widgets alongside a triangle." "That's exactly what it is, and no wonder Phyfe found it had a high frequency. That is nothing more nor less than an explanation of the Stroid concept of the differential. This widget over here must be the sign of the derivative corresponding to our dy/dx." Hastily, Underwood scrawled some symbols on a scratch pad, using combinations of "x"s and "y"s and the strange, unknown symbols of the Stroids. "It checks. They're showing us how to differentiate! Not only that, we have the key to their numerical system in the exponentials, because they've given us the differentiation of a whole series of power expressions here. Now, somewhere we ought to find an integral expression which we could check back with differentiation. Here it is!" * * * * * Terry, left behind now, went to the galley and brewed a steaming pot of coffee and brought it back. He found Underwood staring unseeingly ahead of him into the dark, empty corners of the lab. "What is it?" Terry exclaimed. "What have you found?" "I'm not sure. Do you know what the end product of all this math is?" "What?" "A set of wave equations, but such wave equations as any physicist would be thought crazy to dream up. Yet, in light of some new manipulations introduced by the Stroids, they seem feasible." "What can we do with them?" "We can build a generator and see what kind of stuff comes out of it when we operate it according to this math. The Stroids obviously intended that someone find this and learn to produce the radiation described. For what purpose we can only guess--but we might find out." "Do we have enough equipment aboard to build such a generator?" "I think so. We could cannibalize enough from equipment we already have on hand. Let's try it." Terry hesitated. "I'm not quite sure, but--well, this stuff comes about as near as anything I ever saw to giving me what is commonly known as the creeps. Somehow these Stroids seem too--too _anxious_. That sounds crazy, I know, but there's such alienness here." "Nuts. Let's build their generator and see what they're trying to tell us." _CHAPTER THREE_ Phyfe was exuberant. He not only gave permission to construct the generator, he demanded that all work aboard the lab ship give priority to the new project. The design of the machine was no easy task, for Underwood was a physicist and not an engineer. However, he had two men, Moody and Hansen, in his staff who were first rate engineers. On them fell the chief burden of design after Underwood worked out the rough specifications.