The Raspail microscope can be modified to be either a double (compound) microscope (above) or a single magnifier (below). In the single, or "aquatic" configuration it is similar to the original Raspail microscope.
The single objectives screw into the small object.
Attachment of the single (A) and compound (B) microscope mounts. The horizontal position (arrow) of either microscope is controlled by a thumbscrew and internal screw.
The square shaft of the two microscope mounts fits into the cantilevered arm.