idly over the landscape; and singular wavy lines of light and shade appear upon the ground, the cause of which has not been determined. 377. While an eclipse of the Sun is in its partial phase, the part of the Sun's disk not yet hidden appears as a crescent of greater or less width. When the crescent is very narrow, just before or after the total phase of the eclipse, it often appears to be broken up into detached portions. This effect is considered to be due to the unevenness of the Moon's limb, and to be increased by irradiation. The appearance goes by the name of Baily's Beads, Baily being the name of an astronomer who called attention to this breaking up of the Sun's limb. 378. A few extracts may here be given from the numerous reports made upon the total eclipse visible in the central parts of the United States on August 7, 1869. 379. At Shelbyville, Kentucky, according to Mr. Blake, "about twenty-eight minutes before totality. I noticed that shadows were quite indistinct; that the air was growing chilly; and that the sunlight gave a peculiarly gloomy aspect to the landscape. 380. "Thirteen minutes before totality the air felt quite cold; the Sun appeared as a beautiful crescent, while the black edge of the Moon seemed to stand out from it, giving one the idea of a stereoscopic picture. . . . I was struck by the appearance of the trees to the eastward of the tent, and about fifty feet distant; the foliage was of a peculiar color, very similar to that produced by the electric light.... 381. "Eight minutes before totality, the limbs of the Sun and Moon were shaking violently, and the sunlight was diminished to such an extent that the faces of the observers were of a livid hue, not unlike that of a corpse. Facing to the eastward, I saw that the southern edge of my shadow was comparatively sharp and distinct, while the northern edge was ill-defined and very faint. . . . 382. "The corona, of which, up to this moment" (that of the beginning of the total phase) "there had been positively no indications, now appeared as an extremely soft white light, surrounding the Sun and extending from it, in all directions, to a distance of at least two-thirds of its diameter. There was no appearance of rays, nor was there any sparkling light. . . . 383. "Simultaneously with the appearance of the corona, some of the planets and larger fixed stars became visible to the naked eye. They did not appear as they ordinarily do at night, but seemed to shine with a very soft and slightly diffused white light. The sky, in the vicinity of the Sun, was not blue, as at night, but was of a peculiar milky hue; in the zenith it seemed to be of a purplish tinge, and had a more gloomy aspect; the eastern sky was lighted up with a lurid glare similar to that which sometimes attends an autumn sunset. . . . The darkness was so great that it was impossible to distinguish the foliage of trees a few rods distant." ... 384. General Myer saw the eclipse from the summit of White Top Mountain, in Virginia. According to his account of the appearances noticed during the total phase, "As a centre stood the full and intensely black disk of the Moon, surrounded by the aureola of a soft bright light, through which shot out as if from the circumference of the Moon straight massive silvery rays, seeming distinct and separate from each other, to a distance of two or three diameters of the lunar disk; the whole spectacle showing as upon a background of diffused rose-colored light. This light was most intense and extended furthest at about the centre of the lower limb, the position of the southern prominence. The silvery rays were longest and most prominent at four points of the circumference, two upon the upper and two upon the lower portion. These discrete rays were not visible to me, or did not attract my attention, with the telescope, and the diffused rosecolored light seemed to resolve itself in the field of the glass into the prominences. . . . The sight presented to the unaided eye was the superior in beauty; that through the glass in interest. This was so markedly the case that there was a ... sense of disappointment, on resorting to the telescope, at finding the size and beauty of the spectacle, as seen by the naked eye, so much reduced by the definition of the glass. 385. "The approach of the Moon's shadow did not appear to be marked by any defined line, or movement of any dark column of shade through the air. The darkness fell gradually, shrouding the mountain ranges and the dim world below in most impressive gloom. Our guides had been instructed to watch for the shadow as described, and to call to us at the glasses. They saw nothing of which to give notice. At the same time, and in vivid contrast, the clouds above the horizon were illuminated with a soft radiance; those towards the east with lights like those of a coming dawn, orange and rose prevailing; those northward and westward, as described to us by Mr. Charles Coale, of Abingdon, Virginia, who was present, with rainbow bands of light of varied hues." 386. Mr. Coale's account of this appearance is as follows: "Those who have had the privilege of being upon White Top, and enjoying the westward scene, will remember the grand panoramic view of mountains beginning on the northern and southern horizon, and stretching away to the west till they seem to meet. . . . Stretching along this semicircle of mountains, in long horizontal lines, far below the Sun, lay light and fleecy clouds. . . . At the moment of the falling of the dark shadow, when naught was to be seen above but the stars and the circle of light around the Moon, these clouds became arrayed in all the colors of the rainbow." ... 387. In a letter afterwards written, Mr. Coale says with reference to the preceding description: "I distinctly remember that there were distinct bands of pink, purple, yellow, orange, and fiery red, and each slightly tinged with different shades of its own color. One of the bands, I remember, had to my vision a slight lilac tinge. I do not remember to have observed any green or blue, but I do remember that the lower edge of the purple had a very faint blue tinge." 388. From the preceding accounts we may readily perceive that, when seen under favorable circumstances, the total phase of an eclipse of the Sun presents appearances like those of a fine sunset or sunrise, in addition to the peculiarly interesting spectacles afforded by the dark disk of the Moon surrounded by the light of the Sun's corona, and by the character of the light scattered through the atmosphere around the spectator (375). General Myer's remark, that the use of a telescope lessened the beauty of the appearances seen without one, is generally applicable to astronomical appearances, almost without exception. Telescopes are useful means of acquiring knowledge, when used by persons who understand how to use them to good advantage; but they add little or nothing to the grandeur and beauty of the sky and the stars. Those who imagine that wonderful sights are constantly to be enjoyed by means of astronomical instruments, fail to comprehend what those instruments are made for. To explain this will be one of the chief objects of the following chapters. CHAPTER VIII. GEOMETRICAL TERMS. 389. OUR attention has thus far been mainly directed to various opinions respecting the objects which make up the universe, many of these opinions being firmly established, while others are still under examination by astronomers. To understand how any of them have been formed, we must know something of geometry, of optics, and of the technical terms used in practical astronomy. 390. The object of geometry is the measurement of material objects, or the study of their sizes and shapes. It makes no difference in the geometrical study of any object whether this object is a solid, a liquid, or a gas; whichever it is, it may be called a geometrical solid. The weight, color, and chemical properties of all objects are also left out of sight when the objects are regarded as geometrical solids. A geometrical solid, then, is whatever takes up any space; any part of space, in fact, may be called a geometrical solid, even if it contains no matter. 391. Now if a geometrical solid is cut in two, there is something belonging at once to both of its parts which has shape and size, and yet which does not add any thing to the size of those parts; for they are no larger, when taken together, than the solid from which they were made. This something is called a surface. We are sometimes reminded that the finest statues ever made were already in the blocks of marble from which they were cut, before their sculptors began to make them. In other words, all that is important about a statue is its surface; nobody can make a new material object, but a new surface can easily be made, although it is not easy to make one that is beautiful. The space round any material object may be considered as part of a geometrical solid of |