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244 BLACK APPARATUS FOR MICRO-PROJECTION [Cn. IX
FIG. 138. PROJECTION WITH PHOTOGRAPHIC OBJECTIVES OF 75 TO 125 MM. Focus.
Commencing at the left:
The supply in this case is from the house circuit for a current of five amperes.
There is first a separable attachment plug in the lamp socket. On the table is a separable extension. This is to serve as a safe switch for turning the current on and off.
R Small rheostat for five ampere currents. It is in series, along one wire. In this case it is the positive wire, if direct current is used, and goes to the binding post of the upper or horizontal carbon.
The other wire extends between the binding post of the arc lamp and the separable extension.
The arc lamp with small carbons, in the metal lamp-house. The lamphouse appears transparent as it was in place during only a part of the exposure.
Following the lamp-house is the triple condenser and water-cell (fig. 122).
The stage with the stage water-cell and the mechanical stage of great range (fig. 121, 135).
Support for the photographic projection objective.
All the parts are supported by posts and blocks and all move independently on the baseboard with track. The vertical white lines on the baseboard indicate the proper relative positions of the different blocks.
At the extreme right is shown the adjustable drawing shelf attached to the legs of the table. On this shelf is the projection microscope with three objectives in the revolving nose-piece.
The shield behind the objectives is to prevent stray light from reaching the screen. Demonstration preparations are also shown in the slide box on the shelf.
The projection table with the drawer for holding apparatus is shown with the legs partly removed. The entire table drawn to scale is shown in fig. 182. In this picture the scale is shown by the 10 centimeter rule just above the drawer at the right.