The messages were almost entirely requests for, and answers to requests for, details about the ship plans. The United States had not yet completed a duplicate drive-shaft. Machinists labored to reproduce the cores, which would then have to be wound in the complicated fashion the plans described. But it was an unhappy experience for the scientific minds assigned to duplicate Burke's ship. No woman ever followed a recipe without making some change. Very few physicists can duplicate another's apparatus without itching to change it. There were six copies of the drive under construction at the same time, at the beginning. Four were made by skeptics, who adhered to the original plans with strict accuracy. They were sure they'd prove Burke wrong. Two were "improved" in the making. The four, when finished, worked beautifully. The two doctored versions did not. But still there was fretful discussion of the theory of the drive. It seemed flatly to contradict Newton's law that every action has a reaction of equal moment and opposite sign--a law at least as firmly founded as the law of the conservation of energy. But that had lately been revised into the law of the conservation of energy and matter, which now was gospel. Burke's theory required the Newtonian law to be restated to read "every action of a given force has a reaction of the same force, of the same moment," and so on. When the reaction of one force is converted into another force, the results can be interesting. In fact, one can have a space-drive. But there was bitter resistance to the idea. It was demanded that Burke justify his views in a more reasonable way than by mere demonstration that they worked. After a time, Burke gave up trying to explain things. And when one and then another duplicate drive worked, the argument ceased. But eminent physicists still had a resentful feeling that Burke was cheating on them somehow. Then for days nothing happened. One of the three men in the ship always stayed in the control-chair where he could check the ship's course against the homing signals from the asteroid. He might have to correct it by the fraction of a hair, or swing ship and put on more drive if the radar should show celestial debris in the spaceship's path. Every so many hours the ship had to be swung about so that instead of accelerating she decelerated, or instead of decelerating gained fresh speed. But that was all.