It was found that ray practice was rather complicated. The government had ranges set up in great mountain districts away from any valuable property, but they soon found that spatial warplay could not be carried on on Earth. The rays very quickly demolished the targets, and in a short time made good progress toward demolishing the mountains as well. The problem was solved by using the barren surface of the moon and the asteroid belt beyond Mars as a proving ground. The ships were sent out in squadrons as fast as they could be finished and the men could be brought together and trained. They were establishing a great shield of ships across all that section of the system whence the Nigrans had appeared, and they hoped to intercept the next attack before it reached Earth, for they were certain the next attack would be in full force. Arcot had gone to the conference held on Venus with the other men who had investigated the great wrecks, and each scientist had related his view of things and had offered suggestions. Arcot's idea of the black star was not very favorably received. As he later told Wade and Morey, who had not gone, there was good reason for their objection to his idea. Though the scientists were willing to admit that the invaders must have come from a great distance, and they agreed that they lived in an atmosphere of hydrogen, and judging from their pale skins, that they were not used to the rays of a sun, they still insisted on the theory of an outer planet of Sol. "You remember," explained Arcot, "several years ago there was considerable discussion about the existence of a planet still further out from the sun than Pluto. It is well known that there are a number of irregularities in the orbits of Neptune and Pluto that can't be caused by known planets, and an outer planet could have the necessary mass and orbit to account for them. "This attack from outer space was immediately taken as proof of that theory, and it was very easily supported, too. My one good point that stood for any length of time under their attacks was the fact that those ships weren't developed in a year, nor a century, and that the chemical constitution of the men was so different. There were no new elements discovered, except the light-matter, but they are rather wondering about the great difference of earthly chemical constitution and the constitution of these invaders. "They had one argument that was just about enough to throw mine out, though they pointed to the odds against the thing happening. You know, of course, how planets are formed? They are the results of tidal action on two passing suns.