<P> Microscope slides are often used together with a cover slip or cover glass, a smaller and thinner sheet of glass that is placed over the specimen . Slides are held in place on the microscope's stage by slide clips, slide clamps or a cross-table which is used to achieve precise, remote movement of the slide upon the microscope's stage (such as in an automated / computer operated system, or where touching the slide with fingers is inappropriate either due to the risk of contamination or lack of precision) </P> <P> The origin of the concept was pieces of ivory or bone, containing specimens held between disks of transparent mica, that would slide into the gap between the stage and the objective . These "sliders" were popular in Victorian England until the Royal Microscopical Society introduced the standardized glass microscope slide . </P> <P> A standard microscope slide measures about 75 mm by 25 mm (3" by 1") and is about 1 mm thick . A range of other sizes are available for various special purposes, such as 75 x 50 mm and for geological use, 46 x 27 mm for petrographic studies, and 48 x 28 mm for thin sections . Slides are usually made of common glass and their edges are often finely ground or polished . </P> <P> Microscope slides are usually made of optical quality glass, such as soda lime glass or borosilicate glass, but specialty plastics are also used . Fused quartz slides are often used when ultraviolet transparency is important, e.g. in fluorescence microscopy . </P>

Why does a specimen have to be thin when viewed under a microscope