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CH. X] DRAWING WITH THE MAGIC LANTERN 329
has some sort of device, like a Hooke's jointed rod, so that the lamp may be adjusted without getting up (see fig. 43).
For the arc lamp on the house circuit see Ch. Ill and § 486 below.
§ 463. Other radiants for drawing. — Any of the sources of light discussed in the first six chapters can be used for drawing. One must use the precautions given in those chapters for getting a good screen image by a proper alignment and separation of the elements of the apparatus, and by suiting the darkness of the room to the light.
DRAWING WITH THE MAGIC LANTERN
§ 464. Drawing wall diagrams. — The simplest form of projection for drawing is with the magic lantern. With it the preparation of wall diagrams is very easy (fig. 185).
If one has a lantern slide of the picture or object to be drawn it is put into the lantern as for ordinary projection. The drawingboard is then arranged at a distance to give the desired size, and then all the lines traced with a crayon, a brush or a coarse pen. One can use water colors or paints. For the black nothing is better than India ink.
If one has a smooth wall to which the drawing paper or cloth can be fastened, then the lantern can be moved closer or farther away to get the desired size.
If one has no lantern slide, then a negative may be made of the subject to be drawn, and the negative used in the lantern instead of the lantern slide. The negative should not be too dense or the lines will not come out clearly.
For making negatives to draw from, it is advantageous to use lantern-slide dry plates. These will be of the right size for the lantern and are more transparent than ordinary negatives.
For lettering diagrams nothing is more convenient than the large rubber type found in sets used in advertising and sign making.
§ 465. Getting the desired size. — Any desired size may be obtained by varying the distance between the drawing surface and the projection objective. Either the lantern or the drawing surface or both must be movable.