There is one point about which I need hardly trouble you, although it is worth mentioning in passing. While we produce bright lines in the spectrum of any incandescent substance on this planet, our messages from the stars appear as dark lines. The reason for this is that there are cooler masses of the gases surrounding the incandescent masses forming the stars, and these cooler gases completely absorb the waves we produce. So completely are these waves absorbed that blank spaces are left in the spectrum, and these are the dark lines to which I refer. As they are in the same positions that the bright lines would have occupied had the waves reached the earth, it makes no difference to the reading of our messages. Curiously enough, some of our actions in forming lines in the spectrum led to our actual discovery by man; but I shall tell you of this in the following chapter. CHAPTER XVI HOW MAN PROVED OUR EXISTENCE _THE SCRIBE'S NOTE ON CHAPTER SIXTEEN_ Several men of note declared that "little particles" revolved around the atoms of matter, and that it was the motion of these particles which produced the well-known æther waves of light. This idea was suggested by the result of certain mathematical calculations. It was some time before real experimental proof was obtained. The electron tells its own tale of this great discovery. When the electron speaks of a spectrum line being shifted up or down the scale, it means towards the violet or the red end respectively. We may picture the spectrum as analogous to the keyboard of a piano. In the second part of this chapter, the electron explains how it has enabled man to discover that certain stars are approaching the earth, while others are receding from it. CHAPTER XVI HOW MAN PROVED OUR EXISTENCE We electrons had waited long ages for man to acknowledge our services, but we did not despise the acknowledgment which a few men accorded us upon the basis of their mathematical calculations. It was natural, however, that we should want something more definite than this. You can imagine our joy when real experimental proof of our existence was established. Perhaps you think that we should have been satisfied with this. But even this did not bring acknowledgment from many outside scientific circles, and not even from all within those circles. As our services to man are universal, we feel that all men should become acquainted with our doings. Indeed that was the chief argument used by my fellow-electrons, who urged me to write this autobiography. The story of our actual discovery by man is an interesting one.