Microscope Cover Glass
Thin flat piece of transparent material, usually square or rectangular, about 18x18, 20x20, 22x22, 24x50 wide and a fraction of a millimetre thick, that is placed over objects for viewing with a microscope. The object is usually held between the cover slip and a somewhat thicker microscope slide, which rests on the microscope's stage or slide holder and provides the physical support for the object and slip. The main function of the cover slip is to keep solid specimens pressed flat, and liquid samples shaped into a flat layer of even thickness. This is necessary because high-resolution microscopes have a very narrow region within which they focus.