Microscope
an optical instrument by means of which minute objects are magnified. A double purpose is thus served. Objects too small to be seen by the naked eye become visible. Objects are also enlarged, so that their minute structure may be examined. The invention of the microscope is credited to the Janssen brothers of Holland, somewhere between 1590 and 1609. The supporters of Galileo, to whom the honor of inventing the telescope belongs, claim also that he must have invented the microscope.
Microscopes are of two kinds, simple and compound. The former is merely a double convex lens. When the microscope is held at the right distance from an object, the rays of light coming from the object are caused to converge. They enter the eye as though they came from a larger, more remote object. This enlarged imaginary object is called an image.
In a compound microscope a second lens or set of lenses creates a magnified image of the first image. A simple microscope magnifies from five to twenty diameters, giving from twenty-five to 400 areas. A compound microscope of exceptional power gives as high as 5,000 diameters, or 25,000,000 areas. A pocket lens or magnifying glass may be purchased for twenty-five cents and upward. A serviceable compound microscope suitable for a laboratory costs from fifteen to several thousand dollars.
For a century or two, the microscope was a mere plaything. It is now a necessity. It is an easy matter to adulterate starch, sugar, flour, ground coffee, many drugs, dry paint, and other articles, so as to pass the naked eye; but if a pinch be placed beneath the microscope an expert can identify the particles of different substances with ease. The great advance that has been made in the cure and prevention of typhoid, malaria, yellow fever, scarlet fever, diphtheria, and consumption has been rendered possible by the use of the microscope in studying the bacterial germs or microbes now known to be the causes of these diseases. By placing a scraping of skin, a drop of blood, or other bit of matter under the microscope, the physician is able frequently to determine the nature of the disease with which the patient is afflicted. The microscope enables the expert also to determine whether meat is infested with trichinae. The lens is also used in determining the fineness of cloth. When placed behind a fine wire grating and magnified, it is easy to count the number of threads in a given space.