And because the beams were acted upon by all of the trivia in the Solar System, highly trained technicians stood their tricks at the beam controls. In fifty million miles, even the bending of electromagnetic waves by the Sun's mass had to be considered. Sunspots made known their presence. And the vagaries of land transmission were present in a hundred ways due to the distance and the necessity of concentrating every milliwatt of available power on the target. This problem of the _Empress of Kolain_ was different. Spaceships were invisible, therefore the beam-control man must sight on Mars and the mechanical cam would keep the ship in sight of the beam. The hours went past in a peculiar mixture of speed and slowness. On one hand the minutes sped by swiftly and fleetingly, each tick of the clock adding to the lost moments, never to be regained. Time, being precious, seemed to slip through their fingers like sifting sand. On the other hand, the time that must be spent in preparation of the equipment went slow. Always it was in the future, that time when their experiment must either prove a success or a failure. Always there was another hour of preparatory work before the parabolic reflector was mounted; and then another hour before it swung freely and perfectly in its new mounting. Then the minutes were spent in anticipation of the instant that the power stage of transmitter was tested and the megawatts of ultra-high-frequency energy poured into the single rod that acted as a radiator. It was a singularly disappointing sight. The rod glowed not, and the reflector was the same as it was before the rod drew power. But the meters read and the generators moaned, and the pyrometers in the insulators mounted as the small quantity of energy lost was converted into heat. So the rod drew power, and the parabolic reflector beamed that power into a tight beam and hurled it out on a die-true line. Invisible power that could be used in communications. Then the cam was installed. The time went by even slower then, because the cam must be lapped and polished to absolute perfection, not only of its own surface but to absolute concentricity to the shaft on which it turned. But eventually the job was finished, and the men stood back, their eyes expectantly upon Don Channing and Walt Franks. Don spoke to the man chosen to control the beam. "You can start any time now. Keep her knifed clean, if you can." The man grinned at Channing. "If the devils that roam the void are with us we'll have no trouble. We should all pray for a phrase used by some characters in a magazine I read once: 'Clear ether!' We could use some right now." He applied his eyes to the telescope. He fiddled with the verniers for a brief time, made a major adjustment on a larger handwheel, and then said, without removing his eye from the 'scope, "That's it, Dr. Channing."