CH. X] PROJECTION APPARATUS FOR DRAWING 325 



legs. The supporting brackets are so jointed that the shelf can be let down 

 when the large drawing table needs to be brought up close to the projection 

 table. This method of moving the drawing shelf and lowering it is due to 

 Dr. B. F. Kingsbury. 



As one must sit close to the table, there should be no vertical rail 

 under the front edge to interfere with the knees of the artist. At 

 this edge there is a strengthening piece flat against the top. On 

 the other edge and at the ends are the usual vertical rails. To 

 ensure the rigidity of the table, there are pieces passing across the 

 ends between the legs and near the bottom, and a middle piece 

 extending lengthwise between these end pieces, thus holding the 

 table legs at the two ends, so that they cannot spread either side- 

 wise or endwise (fig. 182). 



The legs are 6 cm. (2^ in.) square, and smooth on the lower end 

 so that the table can be moved easily, or casters may be used. The 

 entire table is finished in dull black and all the corners rounded. 



460. Projection table with drawing shelf. The simplest of 

 all arrangements for drawing with the projection microscope and 

 the magic lantern is a projection table with an adjustable shelf 

 attached to the end (fig. 183, 187). For this arrangement the 

 mirror or prism for reflecting the light downward must be close to 

 the objective or to the end of the microscope. 



As the shelf can be raised to the level of the table top or depressed 

 about 50 cm. (20 in.), it is possible to get quite a range of magnifica- 

 tion from the different image distances alone, using the same objec- 

 tive; but, of course, the upper range is not so great as with a 

 separate drawing table. With the drawing shelf, however, one 

 can get lower powers, as the image can be closer to the end of the 

 objective. By using different objectives one can get all the range 

 desired with either arrangement. The single table and adjustable 

 shelf is, of course, much the cheaper. 



If one uses the table and drawing shelf it is necessary that the 

 apparatus be movable on the optical bench, so that the objective 

 ma}* be beyond the end of the table over the drawing shelf. This 

 is easily accomplished with an optical bench like that shown in fig. 

 158-159. In case one desires a larger drawing surface than the 



