2Ô4 ORDINARY MICROSCOPE FOR PROJECTION [Ch. IX As here shown the substage condenser and mirror have been removed, and also the draw-tube and ocular (see fig. 147, 192 for the ordinary microscope with substage condenser, draw-tube and ocular in position). The lamp, condenser and microscope are on independent blocks and can be moved to any desired position on the baseboard. A The ammeter to indicate the amount of current. R Adjustable rheostat. This rheostat is adjustable between 10 and 20 amperes. The arrow indicates the direction of increase in current. A Adjustable drawing shelf attached to the front legs of the table. In this picture the shelf supports the stage of the projection microscope (fig. 121), and a box of demonstration specimens. The scale of the picture is indicated by the 10 cm. rule just above the table drawer at the right. If the tube of the microscojK? is large it is an advantage, but with the small tube one can do much. If the ocular is not to be used, then it is better to remove the draw-tube so that only the main tube remains. One should be sure that the interior of the tube is dull black (§ 370). § 394. Magic lantern with rods, and an ordinary microscope.— If the magic lantern has the simple construction with rods and feet (fig. 32, 33, 36) an ordinary microscope can be used with it as follows : Remove the rods, bellows and projection objective, and support the arc lamp and the condenser on a block which will lift them high enough so that the microscope in a horizontal position will be in the optic axis. Place all on a baseboard with guides (fig. 146). Clam]) the microscope to a suitable block with grooves or cleats to enable one to move the block accurately along the guides. When properly centered this form of apparatus works well. § 394a. For a water-cell one of the plane-sided glass boxes found on the market can be used, or a cell can be prepared in the laboratory as follows: Select some good plane and clear glass. For the ends of the box make two strips about 2>4 cm. (1 in.) wide and about 10 cm. (4 in.) long. For the sides use two sheets about 10 cm. (4 in.) wide and II cm. (4>i'in.) long; and for the bottom a rather thick sheet or strip about 11 cm. (4>a in.) long and 3 cm. (1 ‘4 in.) wide. The pieces of glass are then put together by placing the bottom on a level table and the other pieces in position and held in place by a string or by narrow strips of gummed paper. The joints are then gone over carefully with an artist’s brush dipped in Ripolin white paint or Valspar varnish. Each coat should be allowed to dry thoroughly before adding the next, that is, for two to five days. Finally one can add water to see if the joints are all tight. If not, dry the glass box and then add more of the Ripolin paint or Valspar varnish.