When there are several units in a town, the beads strung on a long pin or wire can be counted quickly if a bead of a different color is used for every tenth bead, so the whole column may be counted by tens as possible in Fig. 201. A bead map like Fig. 201 should be mounted on several layers of corrugated straw-board to allow the long pins sufficient depth in the mounting to hold fast. For this

MAPS AND PINS

£51

particular map six layers of straw-board were used, giving a total thickness of about l3<t inches. Though this mounting made out of corrugated straw-board was thick, it was extremely light and very convenient to handlco

Fig. 201. Residence of the Men of the Class of 1907, Harvard University, Six Years After Graduation. The Bead Wire for Boston Includes All Men Living within Twenty-five Miles of the City Hall

Beads on long pins and wires were used here when there was more than one man in a town. A white bead was used on the wire for every tenth man. Counting from the top by tens, the exact number in any city can be seen from the illustration. 711 men are represented in this illustration less than 5 inches wide, yet the number in each city can be counted accurately

If long columns of beads must be used as in Fig. 201 for New York and Boston, the beads may be strung on piano wire such as may be secured in any good hardware store. The piano wire should be heated in a gas flame so as to remove some of the spring temper. After the wire has been heated it can be straightened and it will remain straight without continually springing back into coil form.