Plz see the illustrations:

http://www.microscope-microscope.org/basic/microscope-parts....

http://www.microscopy.fsu.edu/primer/anatomy/stage.html

The circular graduated stage, illustrated on the left in Figure 3, is one of the most versatile and useful designs for all types of microscopy and photomicrography.

I am guessing the meaning of "charriot" because of the size of the working area.

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Note added at 1 hr (2009-07-13 23:54:50 GMT)
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Found a drawing of a microscope with the "charriot":
http://ufpel.tche.br/~mgrheing/microscopio.jpg

Apparently, it is the *mechanical stage*, which is mounted on the stage: http://www.greatscopes.com/parts.jpg

Mechanical Stage: A mechanical way to move the slide around on your stage. It consists of a slide holder and two knobs. Turn one knob and the slide moves toward or away from you. Turn the other knob and the slide moves left and right. Since everything is upside down on a (high power) microscope it takes some getting used to but it is very convenient to have one especially when observing moving specimens like protozoans or other pond water critters. Microscopes either have the bolt on mechanical stage that can be added (to many models) at any time or the integral mechanical stage that comes built in to the microscope.
http://www.microscope-microscope.org/basic/microscope-glossa...