MICROSCOPE. As the micrometer enables the man of science to measure very small spaces, so does the microscope afford the means for seeing smaller objects than would other wise be visible. The scientific principles of the microscope are beyond the present work; it is only as a work of construction that it is treated here.
By the term Simple Microscope is meant one in which the object is viewed directly through a lens or combination of lenses. When, however, the magnifying power of the glass is considerable, it requires to be placed. at the proper distance from the object with great precision : it cannot therefore be held. with sufficient accuracy and steadiness by the unassisted hand, but must be mounted in a frame having a rack or screw to move it to wards or from another frame or stage which holds the object. The lens is then called a microscope; and it is furnished, according to circumstances, with lenses and mirrors to col lect and reflect the light upon the object, and with other conveniences.
The Compound Microscope has two lenses which have totally different functions; the first receives the rays from the object, and, bringing them to new foci, forms an image, which the second lens treats as an original object, and magnifies it just as the single microscope magnified the object itself. Each of these purposes is further carried out by an increase in the number of lenses. By means of successive improvements, the Compound Microscope now holds a very high rank among philosophical implements ; while the tran scendant beauties of form, colour, and organi zation which it reveals to us in the minute works of nature, render it subservient to the most delightful and instructive pursuits.
The Solar Microscope consists of a conical tube fixed by its base to a frame of wood, which is screwed to a closed window-shutter, at an aperture purposely made in the shutter : the tube projects into the room, which, when the observations are to be made, is rendered quite dark, and is sometimes lined with black cloth. The magnifying power is produced by a system of lenses contained in the tube, as in other microscopes. On the exterior of the window is a frame carrying a rectangular piece of looking glass, which,by turning on a hinge, is capable of being fixed at any angle with the wall of the building, while, by means of a ring and a rack and pinion, it can be made to turn on the horizontal axis of the instrument, so as to permit the rays of the sun, whatever be the position of the latter, to be reflected into the tube. These rays are made to converge on the object ; and from thence, after refrac tion through the system of object-glasses, they proceed to a screen, on which they depict the magnified image. The solar microscope is now nearly superseded by the Oxyhydrogen Microscope. [LucEnNs_t MicrioscopE.]