Beck 'Ideal' Microscope: the Zentmayer Glide stage:

This stage, a variant of one invented by Joseph Zentmayer, consists of a large glass plate with a large central opening. Attached to the plate is a removable brass slide holder with knobs which both serve as handles, and which have holes to accept accessories like a stage forceps. The glass rides on the raised edges of the circular brass stage. This stage was also offered as an option on the simpler Beck 'Economic' model. It differs from the original form of Zentmayer in that it is mainly made of glass, the glass providing the contact surface with the stage. In Zentmayer's original version, most of this device was made of brass with glass only in a window which was the contact point for the adjustable-tension screw. In addition, Zentmayer's slid on two raised bars of brass, whereas Beck's contact area was the raised edge of the entire circular stage.