CHAP. I. way to those which dealt with the various motions of each member of the starry host: Kepler, Brahe, and Galileo. "Cycle on epicycle, orb on orb," formed the key-note of a large part of astronomy after this time until we come, nearly two thousand years later, to Galileo and his contemporaries, when we again find ourselves in the midst of a sea of speculation on solar matters. Needless to say that this was no accidental circumstance. The telescope had been discovered, and with it at the first essay the visible universe had been infinitely expanded. The period of the invention of the telescope is one of the most interesting and momentous in the scientific history of the world in it the golden age of astronomy may be said to have dawned. We find then living on this planet three immortal men. First Kepler, who by his theory of elliptic motion at one blow swept away the elaborate work of twenty centuries on cycles, epicycles, and excentric motions. Secondly, Tycho Brahe, whose admirable observations formed the groundwork of Kepler's investigations. Lastly, Galileo, who was at home in all branches of science; a man of tremendous mind; who independently, and as it were by the way, invented the telescope, and who was not only the first man who applied it to celestial objects, but perhaps the most illustrious man who ever did so. We all know his reward. Like Anaxagoras, he offended against current dogmas, and in Christendom or Heathendom the penalty for that always was, nay almost is, the same. According to Galileo's own story-and who shall doubt. it? he began the telescope's work on the sun in the 1 The words with which he sent his discovery forth are too admirable not to be quoted in this place:-" I have finished my book. It will be read by the present age or a future one-1 care little which. It can well wait for a reader, for has not God waited 6,000 years for a contemplator of His works?" month of October 1610, being followed by the Jesuit CHAP. I. Scheiner in April 1611, according to his own statement, and by Fabricius in June of the same year. It is pleasant to think that some of the earliest observations of the sun were made by a countryman of our own, and in the Tower of London. I allude to the eminent mathematician Hariot, who observed the spots as early as December 1611, though not as early as December 1610, as was once thought by De Zach.2 Hariot observes spots in 1611. Needless again to say that the old-world answer to our question "What is a Sun?" was at once changed. It was no longer immaculate; no longer, as in the thought of Aris See on the whole question of disputed priority in this matter, "Galilée, sa Vie, ses Découvertes, et ses Travaux." Par le Dr. Max Parchappe. Hachette, 1866. P. 92 et seq. Grant's "History of Physical Astronomy," p. 215. CHAP. I. totle, a material image of the spotless purity of the divine mind. Galileo discovered spots on the brightly shining orb, and the thrill that ran through the world of Schoolmen as a result of this announcement may well be imagined! Galileo's Galileo's discoveries, thanks to the controversy which was raised by the Jesuit Scheiner, who wished to obtain all the credit for Galileo's work, have come down to us in full detail: for to defend himself, Galileo, in a remarkable series of letters to Welser, the chief magistrate of Augsburg, gives us the whole history of his work, which here, however, can only be lightly touched upon. In his first letter, under date May 4, 1612, he states that first letter. the spots are real, as bright as the moon, and composed of matter not very dense and differently shaded; that they are not permanent, but resemble our clouds; and that it is absurd to think they are planets, which was Scheiner's opinion about this time. Second letter. Third letter. In his second letter, dated August 14 in the same year, he refers to their common movements, and to their limitation to zones; states that they lie near the sun, and move on it and not above it; and then announces, from observations of them made near the sun's edge, first, that they are deep and of various depths, and secondly, that their blackness diminishes near the edge. In his third letter, written on the 10th of December, 1612, he demonstrates the sun's rotation, and assigns a period not far from that given by modern observation. Scheiner, who wrote under the signature of Apelles latens post tabulam, to the same Welser, held on his side that the spots were similar to Jupiter's moons, or probably to the strange things which Galileo had then recently discovered round Saturn, or that they might be comets. He held that it was impossible they could be on the sun itself, and imagined some to be as far from the sun as the Moon, Venus, or Mercury (on the Ptolemaic system). At the same time he pointed out that they are thin, to account for their oval appearance near the limb, adding that they are not fixed stars, although they CHAP. I. are as dense as the moon. It is not necessary in this brief sketch to do more than refer to the detailed work of Scheiner recorded in his "Rosa Ursina," or to the subsequent observations of Fabricius and Hevelius. It is clear that the answer to our question was now much closer; indeed we have the spots and no longer the sun itself, due to evaporations and exhalations, the luminary itself being described as a "liquor igneus. . . quasi vastissimum luminum pelagus et mare igneus, quod suos habet abyssos, occultos meatus voragines atque vortices." Our next step carries us to 1774; for in De la Hire's memoir presented to the Paris Academy in 1704, there is nothing that calls for remark. work. F. Explanation of Sun-spots on Wilson's hypothesis-of a solid, dark sun and cloudy ente pe A and c, spots as seen near sun's centre and edge. (See text for explanation.) In 1774, Dr. Wilson of Glasgow communicated a paper Wilson's to the Royal Society, demonstrating that the spots were The reader may with profit consult Grant's "History of Physical Astronomy," p. 213 et seq. 2 Phil. Trans. 1744. Wilson's work. CHAP. I. cavities in a luminous envelope surrounding the sun, which, according to him, was a dark globe. His observations were made on the great sun-spot of 1769. The reasoning on which he based his idea of the cavernous nature of the spots will easily be gathered from an inspection of the woodcut, Fig. 2: it will be seen that it depends upon the different appearances put on by the same spot as seen in the centre of the disc and near the sun's limb. In the case of a spot, supposed round, seen in the first position, it is clear that we shall have a round, black shade in the centre, equally surrounded by a half-tone; while when the spot is near the limb it is equally clear that on this hypothesis the central black shade will be almost entirely hidden, and the half-tone quite hidden on one side and largely developed on the other. Now this is exactly what is observed. De la Lande. Sir Wm. Herschel's work. To this paper of Wilson's, which is now acknowledged to be one of the most important contributions to our knowledge of the sun, in 1776 De la Lande replied in a paper presented to the Paris Academy. He does not agree with Wilson, although he gives up the idea which he had formerly held, that the spots were masses of scoriæ, and then he adds:-"J'ai donc pensé que les taches étaient plutôt les éminences d'un noyau solide, decouvertes et recouvertes alternativement par le flux et le reflux de la matière ignée où elles sont presque toujours plongées. . . les nebulosités [faculæ] qui environnent les taches et qui ressemblent à des bancs de sable présentent l'idée d'un basfond qu'on aperçoit à l'endroit où la matière fluide a moins de profondeur." We must last of all in this chapter deal with Sir William Herschel's answer to the question at the head of it. Aided by telescopes of his own manufacture, he doubtless was the first man on our planet to see the sun in all its beauty and detail, as it is now seen with even small instruments of modern make. 1 Phil. Trans. 1795. |