The flashlights, equipped as they were with storage coils for power, were actually powerful searchlights, but in the airlessness of space, the rays were absolutely invisible. They could only be seen when they hit the relux inner wall at such an angle that they were reflected directly into the observer's eyes. The lux metal wall, being transparent, was naturally invisible, and the smooth relux, reflecting one hundred percent of the incident light, did not become illuminated, for illumination is the result of the scattering of light. It was necessary to look closely and pass the beams over every square inch of the surface. However, a crack would be rough, and hence would scatter light and be even more readily visible than otherwise. To their great relief, after an hour and a half of careful inspection, none of them had found any signs of a crack, and they went back into the ship to resume the voyage. Again they hurled through space, the twin ghost ships following them closely. Hour after hour the ship went on. Now they had something else to do. They were at work calculating some problems that Arcot had suggested in connection with the velocities of motion that had been observed in the stars at the edge of the island universe they were approaching. Since these stars revolved about the mass of the entire galaxy, it was possible to calculate the mass of the entire universe by averaging the values from several stars. Their results were not exact, but they were reliable enough. They found the universe to have a mass of two hundred and fifty million suns, only a little less than the home Galaxy. It was an average-sized nebula. Still the hours dragged as they came gradually nearer their goal--gradually, despite their speed of twenty-four light years per second! At the end of the second day after their trouble with the cosmic ray field, they stopped for observation. They were now so near the Island Universe that the stars spread out in a huge disc ahead of them. "About three hundred thousand light years distant, I should guess," said Morey. "We know our velocity fairly accurately," said Wade. "Why can't we calculate the distance between two of these stars and then go on in?" "Good idea," agreed Arcot. "Take the angle, will you, Morey? I'll swing the ship." After taking their measurements, they advanced for one hour. Knowing this distance from experience, they were able to calculate the diameter of this galaxy. It turned out to be on the order of ninety thousand light years.