Besides regular movements to right and left, up and down, to and from us--changes in the intensity of illumination by changes of distance--besides variations occurring at regular and ascertainable intervals, there are stars called _temporary_, shining awhile and then disappearing; _new_, coming to a definite brightness, and so remaining; and _lost_, those whose first appearance was not observed, but which have utterly disappeared. In November, 1572, a new star blazed out in Cassiopeia. Its place is shown in Fig. 67, ch g being the stars d * g ch in the seat of the chair, and d being the first one in the back. This star was visible at noonday, and was brighter than any other star in the heavens. In January, 1573, it was less bright than Jupiter; in April it was below the second magnitude, and the last of May it utterly disappeared. It was as variable in color as in brilliancy. During its first two months, the period of greatest brightness, it was dazzling white, then became yellow, and finally as red as Mars or Aldebaran, and so expired. A bright star was seen very near to the place of the _Pilgrim_, as the star of 1572 was called, in A.D. 945 and 1264. A star of the tenth magnitude is now seen brightening slowly almost exactly in the same place. It is possible that this is a variable star of a period of about three hundred and ten years, and will blaze out again about 1885. But we have had, within a few years, fine opportunities [Page 224] to study, with improved instruments, two new stars; On the evening of May 12th, 1866, a star of the second magnitude was observed in the Northern Crown, where no star above the fifth magnitude had been twenty-four hours before. In Argelander's chart a star of the tenth magnitude occupies the place. May 13th it had declined to the third magnitude, May 16th to the fourth, May 17th to the fifth, May 19th to the seventh, May 31st to the ninth, and has since diminished to the tenth. The spectroscope showed it to be a star in the usual condition; but through the usual colored spectrum, crossed with bright lines, shone four bright lines, two of which indicated glowing hydrogen. Here was plenty of proof that an unusual amount of this gas had given this sun its sudden flame. As the hydrogen burned out the star grew dim. Two theories immediately presented themselves: First, that vast volumes had been liberated from within the orb by some sudden breaking up of the doors of its great deeps; or, second, this star had precipitated upon itself, by attraction, some other sun or planet, the force of whose impact had been changed into heat. Though we see the liberated hydrogen of our sun burst up with sudden flame, it can hardly be supposed that enough could be liberated at once to increase the light and heat one hundred-fold.