As Tom and Dorothy bent over the instrument, I asked Hamerly, “What do you expect to find from the spectroscope? What does it do?” “It breaks down light,” answered Hamerly, “by means of a prism, as a prismatic chandelier or a prismatic glass thermometer throws the spectrum of a sunbeam on the floor, breaking the white light of the sun into a shifting mass of color that changes from red, through orange and green to violet. Every different glowing gas gives off a slightly different light. We can tell by the spectroscope whether the light from this gas is the same as any we have known before, or whether it is different. If the light waves sent out are unlike any recognized before, we can be sure we have a new gas.” Tom was turning a screw, with his eye glued to a small telescope. “Change that tube a bit to the right, Hamerly,” he said, and it was changed. “Now a bit higher. No, not so high, a bit lower now. There you are.” He gazed long and intently, then rose, motioning Hamerly in silence to take his place. Dorothy followed Hamerly, and Swenton followed her. I ended, but I could distinguish nothing save some lines crossing a scale placed within the tube. As I rose from the stool, Tom reached up to throw on the lights. As he faced around, Hamerly met him with outstretched hand. “It is only given to a handful of scientists in a century,” he said, “to find a new element, to discover one of those units from which the world is made. I believe you have done it this afternoon.” “It is a new, elementary gas,” said Dorothy. “You found it, Tom, when you climbed that table.” “Much good it will do me, so far as that goes,” remarked Tom. “So far as we know, all there is of it in the world is in this tube. I don’t know how to produce any more, and I can’t publish anything about it, for it would interfere with our search for the man.” “You have no right to say that it’s no use,” said Dorothy. “Again and again as we have gone on, the slightest unexpected things have come to mean the most. I believe this tube of unknown gas may be a most important link in the chain.” “All right,” said Tom. “Just as you say. You can be sure I wasn’t going to throw it into the waste basket.” While Swenton cleared away, the rest of us went into the wooden room. Hamerly passed across and opened one of the wooden shutters. “The fog is lifting,” he said. We looked out and saw that the other side of the street was gradually becoming visible. Dorothy seated herself by the window, and we joined her. “I don’t know that there could be a better time,” I began, “than right here and now, to find out just where we are. For my part, I want to understand the relation between the new gas and all that has gone before. If we bring all our information together, won’t there be a better chance to get a line on our next move?”