exertion to complete it; but he was speedily rewarded. Soon after, some say on the very day it was finished, he discovered the sixth satellite of Saturn; and, a few months afterwards, the seventh. Astronomers of the present day hope that new discoveries may yet be made by means of what they call a fluid-lens, (that is, a lens composed of two glasses, with a liquid between them,) if king William the Fourth will extend such patronage to the inventor as Dr. Herschel experienced from George the Third.+ * Dr. Hutton and Joyce do not exactly agree on this point. 155 LECTURE V. MICROSCOPES AND CAMERA-OBSCURA. As the telescope derived its name from affording a view of distant objects, the Greek word mikros, small, was appropriated to that instrument, which is especially designed for taking a view of small things. Any contrivance which renders minute objects visible and distinct, by enabling us to look at them very closely, is, in fact, a microscope, though we are in the habit of using that word as the name of a complicated instrument. You know that a man at the other end of the street, or a house viewed at the distance of halfa-mile, appears very much smaller than any man or house is in reality; but are you aware 156 A SIMPLE MAGNIFIER. that if you could see any small object, a fly, for instance, when it was almost close to your eye, it would appear larger than the distant house or man. You think, perhaps, that an object will not appear magnified unless we look at it through a magnifying-glass; but I will convince you that this is a mistaken notion. Probably none of you can read if you hold a book within six inches of the eye; but if you are enabled to distinguish the letters at half that distance, they will appear to be twice the size, even though no magnifying-glass is employed. I have pricked a hole in this piece of brown paper; will one of you take a book and try to read, by looking through it? Here is no lens, no contrivance, but a simple pinhole; and the letters appear magnified, only because you are enabled to distinguish them at a shorter distance. I have now made a hole with a much smaller pin; and you will find that the letters are still more magnified, but less distinct than before, because too little light passes through that minute hole to form a clear image |