Just why these dark lines appear would take us too far afield to explain here; suffice it to say that every chemical element has been found to yield a different spectrum; that is to say, the number and arrangement of these dark lines will indicate the presence of the element in question. Whenever certain lines appear on the spectrum, we may be sure that such-and-such an element is present. Thus, Kirchhoff first proved that two of these dark lines were caused by the white light of the solar photosphere having suffered absorption at the sun, by passing through a stratum of glowing sodium vapor. Sodium was thus shown to be present in the sun. Other elements were similarly identified, not only in the sun, but in the millions of stars in the heavens. By means of spectrum analysis, therefore, it has been possible to detect and identify the various chemical elements present in any given sun or star in space. ASTRO-PHYSICS AND CHEMISTRY In this manner, about forty terrestrial elements have been shown to exist in the sun. Carbon, oxygen, iron, silicon, nickel, etc., exist in the sun just as they do on our earth. On the other hand, many elements, such as mercury, nitrogen, sulphur, and boron do not appear, although they are found in abundance on the earth. Yet several elements were shown to exist in the sun which up to that time had not been discovered here. Helium is an example. (From the Greek, _Helios_, the Sun). And yet, when attention was directed to this element, it was soon found in our earth, and is today so common that helium gas is employed to inflate balloons, in preference to hydrogen, on account of its non-combustibility. SPECTRUM ANALYSIS Spectrum analysis, then, tells us the precise chemical constitution of the various suns, or stars, in space, and it also tells us that these stars are incapable of supporting life such as we know it. As Dr. E. Walter Maunder says, in his book, “Are the Planets Inhabited?”: