Page:Graphic methods for presenting facts (1914).djvu/272

 Brass wire should be used if the holes in the beads are large enough to take wire of a diameter sufficient to give the required amount of stiffness. Brass wire is not as stiff as steel wire. When small beads must be used having small holes, the combination of wire and beads may be given several coats of varnish, if necessary, to make a tall bead column stand up straight. The columns for Boston and New York in Fig. 201 had to be varnished as the wire was very small on account of the fact that the diameter of the beads was only about 3/32 inch.

The bead map in Fig. 201 gives a great quantity of information in a small amount of space. The illustration depicts the whole United States on a page width of only 5-1/8 inches, yet all the facts represented by the beads are brought out clearly. The men of the group portrayed who reside in foreign countries are indicated by pins near the seacoast with arrows pointing toward the country of residence. The fact that there were large numbers of the men in Massachusetts made necessary an extremely long wire for the beads of the Boston district. Because of the small size of the finished illustration and the size of map available, large diameter beads could not be used, and the bead wire for the Boston district was necessarily very tall and slender. The Boston bead column was about as tall as could be used without the column of beads bending under its own weight, even with the bead column varnished.

Another difficulty in having very tall columns of beads is due to the fact that the bead map must be photographed at an angle of about 45 degrees in order to show a good picture of the map.

If the bead column projects more than a reasonable distance from the map it is impossible to find a camera lens which will keep in focus the whole map and the full length of the bead columns. Either the map or the top of the bead column will be out of focus and there is no way of overcoming the difficulty. When Fig. 201 was photographed the image on the ground glass of the camera showed at once that the tops of the bead columns were out of focus. The bead wires for New York and for Boston were accordingly pulled entirely out of the map and the map was photographed without these two bead wires. The two bead columns were drawn in by hand on the surface of a photograph measuring 8 inches across the base of the map. With a little care, using a fine-pointed pen, bead columns such as these can be drawn in so that the ordinary observer would never notice that