THE MICROSCOPE. BEING THE ARTICLE CONTRIBUTED BY ANDREW ROSS TO THE “PENNY CYCLOPÆDIA,” PUBLISHED BY THE SOCIETY FOR THE DIFFUSION OF USEFUL KNOWLEDGE. FULLY ILLUSTRATED. NEW YORK: THE INDUSTRIAL PUBLICATION COMPANY. 1877. THE MICROSCOPE. Microscope, the name of an instrument for enabling the eye to see distinctly objects which are placed at a very short distance from it, or to see magnified images of small objects, and therefore to see smaller objects than would otherwise be visible. The name is derived from the two Greek words, expressing this property, MIKROS, _small_, and SKOPEO, _to see_. So little is known of the early history of the microscope, and so certain is it that the magnifying power of lenses must have been discovered as soon as lenses were made, that there is no reason for hazarding any doubtful speculations on the question of discovery. We shall proceed therefore at once to describe the simplest forms of microscopes, to explain their later and more important improvements, and finally to exhibit the instrument in its present perfect state. In doing this we shall assume that the reader is familiar with the information contained in the articles “Light,” “Lens,” “Achromatic,” “Aberration,” and the other sub-divisions of the science of Optics, which are treated of in this work. The use of the term _magnifying_ has led many into a misconception of the nature of the effect produced by convex lenses. It is not always understood that the so-called magnifying power of a lens applied to the eye, as in a microscope, is derived from its enabling the eye to approach more nearly to its object than would otherwise be compatible with distinct vision. The common occurrence of walking across the street to read a bill is in fact magnifying the bill by approach; and the observer, at every step he takes, makes a change in the optical arrangement of his eye, to adapt it to the lessening distance between himself and the object of his inquiry. This power of spontaneous adjustment is so unconsciously exerted, that unless the attention be called to it by circumstances, we are totally unaware of its exercise.