MICROSCOPE (from Gk. tusp6s, m ikros, small + skopein, to view). An instru ment by which objects are made to appear of greater magnitude. Undoubtedly the oldest mi croscope on record is a plano-eonvex lens of quartz found by A. H. Layard amid the ruins of Nineveh, surrounded by articles of bronze and other materials. It is now in the British Mu seum, and is 0.5 em. (less than 0.2 inch) in thickness, 3.5 cm. (1.4 inches) in diameter, and its focal length is 10.7 cm. (about 4 inches). Many authorities believe with good reason that this lens was used as a burning glass, as similar ones were used for that purpose at the time of Socrates. On the other hand. there can be no doubt that such lenses were used as simple micro scopes, or magnifying glasses, inasmuch as the ap parent increase of size of an object seen through them must inevitably have attracted the atten tion of such good observers, and moreover the elaborate and delicate engraving on many of the and gems of that period furnish sufficient evidence that some means must have been em ployed to aid the eye in executing this work. Spherical glass vessels filled with water would also have called attention to their employment as magnifiers: spherical drop., of glass would act similarly.
During the later Middle Ages sueh simple 1etkes came more and more into use, especially as aids to the eye in ordinary vision, as spec tacles. _pectaele-make• of Miffilelburg, land, Zacharias Janssen, undoubtedly was the first to build a compound miscroscope, and about 1500 constructed such an instrument and presented it to Charles Albert. .:Nrchduke of Austria. It was nearly six feet long, supported upon brass dolphins on all (bony board. It con tained only two lenses. Robert llooke (1635 1703). secretary of the Royal Society, made many improvements in the construction and use of the microscope, and Divini in 1668 improved the instrument by using two plano-convex lenses as an eyepiece (see below). in 1686 Campani improved the form of the instrument and intro duced the use of a screw for proper focusing.
Nevertheless the of the microscope took a different direction, on account of the seri 0115 difficulties with aberration (q.v.) in short focus lenses, and under the influence of Leeuwen hock attention was returned to the development of the simple microscope. Antony von Leeuwen hoek (1632-1723) constructed very efficient and convenient simple miseroscopes, developing the method already tried by 'Hooke and Hartsoeker of making high-power lenses by allowing a drop of molten glass to occupy a small hole in a plate of brass. Even a drop of water or oil was also used in this way. Lecuwenhoek is said to have made 247 miscroscopes, observing the circula tion of the blood in the feet of frogs, spermatozoa, and many other interesting things. To this pe riod belong also the names of Wilson (1708-88), Hartsoeke• (1656-1724), Stephen Gray ( ?-1736), Jan van Mussehenbroek (1687-1748), Lentmann (1667-1736), and others, About this time Samuel Reyher (1635-1714) employed such a lens to project an image upon the wall, or a screen, using the sunlight for illumination, and is thus probably the inventor of the 'solar microscope.' Rake• ( 1608-1774) with the aid of the mechanic Searlcit constructed in 1736 a catoptrie miscroseope, using mirrors in stead of lenses in a manner suggested by the Gregorian telescope. But such instruments never came to he of much importance, since Dolland (1706-61) in 1757 confirmed the theoretical con clusions of Euler (1707-83) and Klingenstierna (108-1765) that for the 511 IIIP refraction the dispersion might he different, and thereupon pro ceeded to construct an achromatic objective, that is, a lens in which the eolor effeets are elimi nated by the use of two kinds of glass. Ne•er theless, the great difficulty of grinding sue]) small lenses with sufficient accuracy for the correction of the errors due to aberration prevented their use in a !flannel' Id all commensurate with their successful employnallt in astrollotuieal telescopes.