We do not know exactly when man first discovered that objects seemed much larger when seen through a specially shaped piece of glass. There are some very old stories but they are all vague. The known history of the microscope begins in the seventeenth century when the Dutchman, Anton van Leeuwenhoek, invented a simple microscope consisting of a single lens with a relatively high magnification. The first compound microscope was devised in 1590 by Zacharias Janssen.

The word microscope comes from the Greek micros meaning small and skopeein meaning ‘to look’. The instrument works with two lenses or discs of glass. The upper lens is the eyepiece and the lower one is the objective. The objective lens magnifies the object and the eyepiece lens enlarges the magnification. In modern instruments both the eyepiece and the objective consist of several lenses, so arranged that they rectify the distortion caused by the curvature of the glass.

The objects to be examined are placed on a glass slide. These objects are cut very thin so that light shines through them. In a microscope the light is reflected through the objects by a mirror. Scientists also use electronic microscopes which can magnify objects millions of times.

The basic parts of a microscope are the condenser which illuminates; the focusing mechanisms operated by coarse or fine adjusting screws; and a variable diaphragm that controls the amount of light that goes into the condenser.