Page:Popular Science Monthly Volume 5.djvu/552

534 We must, then, look at the sun with no more idea of witnessing any thing without the sphere of natural laws, than in looking at a fire across the street. It need not follow that we shall find the operation of those laws exactly the same that our limited experience has presented, and we shall still find abundant cause for admiration and wonder without introducing mysteries of our own creation.

When we telescopically examine that brilliant surface which we see daily with the naked eye (the photosphere), to study such of its phenomena as are here described, we do not need the spectroscope, but some means of protecting the eye from the blinding light and heat, and this should not involve the use of any colored shades. If we look into an unsilvered glass, as, for instance, into the panes of a shop-window from the street, we observe that it acts as a mirror, sending back a feeble reflection of ourselves, or other objects without; most of the rays from which have gone altogether through the glass, while a comparative few are returned to form the image. It may occur to us, then, instead of looking directly at the solar image formed by our telescope, to let it fall on a piece of plain glass, placed diagonally, through which about nineteen parts in twenty of the light will pass and be thrown away, the remaining twentieth being reflected and forming an exact though enfeebled image.

When this has been done, if the reflected image be still too bright, we may reflect it again, this time only a twentieth of the first twentieth reaching the eye, and so on to any degree; but it is strikingly illustrative of the intensity of the solar splendor that, when, by three such reflections, the sunlight has been enfeebled 8,000 times, we yet find it intolerably bright. Instead of more mirrors, it is better to now arrange that the third mirror may rotate, so as to polarize the light. When this is done, the image of the sun appears distinct (if the optician have done his work well), colorless, and of any brightness desired.

The instrument just described in general terms is known as the polarizing eye-piece. All danger and discomfort in studying the sun disappear with its use, and we may look at its unclouded face as though the eye had been strengthened to bear its light; in fact, many hours of scrutiny of the solar disk with this instrument wearies the eye less than a few minutes' telescopic examination of the moon does without it.

What we shall see with it is far from being that sphere of dazzling light, everywhere equally brilliant, which we have been accustomed to consider the sun. The eye ranges over a vast surface, presenting at one view over five thousand times the entire area of our globe, to find everywhere diversity of shade. It is not only darker near the edges than at the centre, but the whole (apart from any consideration of the spots) presents an appearance somewhat like that very peculiar one which the ocean has when we obtain a bird's-eye view of it from some great height.