MICROSCOPE

(Yunanca köken — orijinale bakınız.) An optical instrument which enables us to see and examine objects which are too minute to be seen by the naked eye. Microscopes are single or compound, according to the nature of their construction; a single microscope being one through which, whether it consists of a single lens or a combination of lenses, the object is viewed directly; and a compound microscope one in which two or more lenses are so arranged that an enlarged image of the object formed by one of them is magnified by the second, or by the others, if there are more than two, and seen as if it were the object itself. Single Microscope. — This instrument is, for the most part, simply a lens or sphere of any transparent substance, which refracts the rays of light i uing from a small body placed in its focus, and gives them such a degree of convergency as is nece ary for distinct vision. In order that the rays of light i uing from the several points of a very small body may produce a sensible impre ion on the retina of the eye, it is nece ary that the object be brought very near the eye; but when this is done, the rays coming from its different points are so divergent as to produce only a confused image. Now, if a convex lens be interposed between the object and the eye, and so placed that its distance from the object is a little le than its focal distance, the diverging rays i uing from the object are refracted by the lens, and enter the eye placed behind it, either parallel, or so nearly parallel as to afford distinct vision. The object is then seen in the direction of the refracted rays, and at the distance at which it could be distinctly seen by the naked eye; and consequently magnified in the ratio of the distance of distinct vision to the focal distance of the lens. This 3B 2 [s. 752]