The earliest microscopes are called simple microscopes or the ‘single’ type, using only a single lens. The hand lens or ‘loop’ is the modern low-magnification equivalent. The lenses of the first simple microscopes were usually encased in metal, ivory, tortoise shell, horn or wood with a small handle, or mounted in a brass plate like the Leeuwenhoek microscope. Lenses ground to 1/10 inch diameter can magnify up to 100x, and some early lenses were actually made of polished beads of glass. The first simple microscope ever known to be on display was in a London exhibition in 1619, and the earliest illustration known is Isaac Beeckman’s drawing of a ‘microscopium’ in 1631. The simple microscope works by holding the lens right next to the eye and bringing the object of study close to it. The tiny high power lenses could be used best with transmitted light. The compass microscope used a hinge between a handle and the plate and a ring to hold interchangeable lenses of differing magnification. On the screw barrel type of simple microscope the barrel is screwed up or down to bring the specimen into the focal plane of the lens. They were usually mounted to a handle or came with a collapsible stand. Simple microscopes were sometimes mounted to a post on a stand, an arrangement called ‘botanical pattern’ today. Aquatic microscopes with glass stages on which to place water samples and dissecting microscopes with wood or brass stages and sub-stage reflecting mirrors were produced from the mid-1700s.