In a total solar eclipse, the time which elapses from the moment when the moon's disc first begins to impinge upon that of the sun at his western edge until the eclipse becomes total, lasts about an hour. During all this time the black lunar disc may be watched making its way steadily across the solar face. Notwithstanding the gradual obscuration of the sun, one does not notice much diminution of light until about three-quarters of his disc are covered. Then a wan, unearthly appearance begins to pervade all things, the temperature falls noticeably, and nature seems to halt in expectation of the coming of something unusual. The decreasing portion of sun becomes more and more narrow, until at length it is reduced to a crescent-shaped strip of exceeding fineness. Strange, ill-defined, flickering shadows (known as "Shadow Bands") may at this moment be seen chasing each other across any white expanse such as a wall, a building, or a sheet stretched upon the ground. The western side of the sky has now assumed an appearance dark and lowering, as if a rainstorm of great violence were approaching. This is caused by the mighty mass of the lunar shadow sweeping rapidly along. It flies onward at the terrific velocity of about half a mile a second. If the gradually diminishing crescent of sun be now watched through a telescope, the observer will notice that it does not eventually vanish all at once, as he might have expected. Rather, it breaks up first of all along its length into a series of brilliant dots, known as "Baily's Beads." The reason of this phenomenon is perhaps not entirely agreed upon, but the majority of astronomers incline to the opinion that the so-called "beads" are merely the last remnants of sunlight peeping between those lunar mountain peaks which happen at the moment to fringe the advancing edge of the moon. The beads are no sooner formed than they rapidly disappear one after the other, after which no portion of the solar surface is left to view, and the eclipse is now total (see Fig. 5). [Illustration: _In a total Eclipse_ _In an annular Eclipse_ FIG. 5.--"Baily's Beads."] But with the disappearance of the sun there springs into view a new and strange appearance, ordinarily unseen because of the blaze of sunlight. It is a kind of aureole, or halo, pearly white in colour, which is seen to surround the black disc of the moon. This white radiance is none other than the celebrated phenomenon widely known as the _Solar Corona_. It was once upon a time thought to belong to the moon, and to be perhaps a lunar atmosphere illuminated by the sunlight shining through it from behind. But the suddenness with which the moon always blots out stars when occulting them, has amply proved that she possesses no atmosphere worth speaking about. It is now, however, satisfactorily determined that the corona belongs to the sun, for during the short time that it remains in view the black body of the moon can be seen creeping across it.