As the small quantity of this grew after another week of collecting, it was treated to remove the ordinary carbon particles and accumulated pollens. When this was done there was very little remaining, but that little something might be ordinary dust carried into the atmosphere from the surface of the Earth. Or it might be out of the tail of the comet. Dust from the stars. By now, Ken and his companions had learned the use of the electron microscope and how to prepare specimens for it. When their samples of dust had become sufficient they prepared a dozen slides for photographing with the instrument. As these were at last developed in the darkroom, Ken scanned them eagerly. Actually, he did not know what he was looking for. None of them did. The prints seemed to show little more than shapeless patches. In the light of the laboratory he called Joe Walton's attention to one picture. "Look," he said. "Ever see anything like that before?" Joe started to shake his head. Then he gave an exclamation. "Hey, they look like the same particles found in the metals, which nobody has been able to identify yet!" Ken nodded. "It could be. Maybe this will get us only a horselaugh for our trouble, but let's see what they think." They went into the next laboratory and laid the prints before Ken's father and his associates. Ken knew at once, from the expressions on the men's faces, that they were not going to be laughed at. "I think there may be something here," said Professor Maddox, trying to suppress his excitement. "It is very difficult to tell in a picture like this whether one particle is similar to any other, but their size and configuration are very much alike." Professor Douglas grunted disdainfully. "Impossible!" With that dismissal, he moved away. Professor Larsen looked more carefully. "You could scrape dust from a thousand different sources and get pictures like this from half of them perhaps. Only the chemical tests will show us the nature of this material. I am certain it is very worthwhile following up." "I feel certain that whatever contaminating agent we are dealing with is airborne," said Professor Maddox. "If this is the same substance it will not tell us its origin, of course, nor will it even prove it is responsible for these effects. However it is a step in the right direction. We can certainly stand that!" "Couldn't we tell by spectroscopic analysis?" said Ken. "That would be difficult to say. The commonness of the elements involved might mask what you are looking for. Get John Vickers to help you set up equipment for making some comparisons."