"Admitted," he said. "But I'd like to have one, anyway. Look, Evans, how does this thing work?"
"On a magneto-gravitic principle. Gravity, I am beginning to understand, is not a matter of wave propagation at all. It is a factor of matter—and it is either there or it isn't."
"I wouldn't know."
"Well, that's the theory. So we utilize an artificial manifestation of gravity, beamed. It also seems that gravitational effects are mutual. In other words, the attraction between Terra and Sol is the combination of mutual attractions. So our beam, increasing the attraction between the object and the beam also causes the increase of the attraction between the beam and the object. For beam read transmitter; I always think of the radiating element as being the beam instead of what I should. Anyway, when the attraction is increased, it affects a detector in the radiating elements. That gives you your indication."
"How about ranging."
"Still a matter of the inverse-square of the distance. We know accurately the attraction-factor of our beam. Whatever reflects will have distance-diminishment which we can measure and use."
"But it is also proportional to the mass, isn't it?" asked Barden.
"It'll take a nice bunch of circuits," grinned Evans, "but we can check the mass with another beam's attraction to it and differentiate. An integrating system will solve for range on the basis of mass and distance. The celestial search and presentation systems will be the same."
"O.K.—how about communications?"
"Sure," said Evans.