Microscope

A microscope is an instrument that enables the user to view objects smaller than can be seen with the naked eye. The word usually refers to an optical compound microscope. Other kinds of microscopes will be discussed later.

Optical compound microscopes

Optical compound microscopes are somewhat similar to telescopes in that their basic design is a tube, with holding a lens or a system of lenses at each end of the tube. A microscope consists of an ocular or eyepiece that you look into, and an objective which is close to the object that is being observed.

Such microscopes can magnify from about 10 to 1000 times.

The higher powers, however, require special techniques; the object to be observed must be prepared as a flat, thin section, usually stained with special chemicals to make transparent structures visible, cemented under a cover-glass, and used with a special oil-immersion objective, with a drop of oil between the objective and the cover slip. Microscopes in children's science kits may claim high magnifications, but anything over about 50X is "empty magnification" and of no use.

Phase contrast microscopes

Many biological structures consist of thin, transparent, jellylike material, surrounded by water-like fluid. Even when magnified, such structures are difficult or impossible to see, because they do not affect light very much. Anyone who has ever dropped a contact lens into water should understand this. The traditional method for seeing these structures, developed in the 1900s, was to fix them (kill and harden them) with an agent like formadehyde or glutaraldehyde, and then treat them chemical dyes and stains. In the twentieth century, optical methods were developed that made these structures visible without staining. This was an important breakthrough, particularly in allowing the study of living cells.