6,700,000 6,600,000 6,500,000 6,400,000 6,300,000 6,200,000 6,100,000 6,000,000 5,900,000 6,800,000 5,700,000 6,600,000 5,600,000 5,400,000 5,300,000 5,200,000 5,100,000 6,000,000 4,300,000 4,800,000 4,700,000 4,600,000 4,500,000 4,400,000 4,300,000 4,200,000 4,100,000 4,000,000 3,900,000 3,800,000 3,700,000 3,600,000 3,600,000 3,400,000 3,300,000 3,200,000 3,100,000 3,000,000 2,900,000 2,800,000 2,700,000 2,600,000 2,600,000 2,400,000 2,300,000 2,200,000 2,100,000 2,000,000 1,900,000 1,800,000 1,700,000 1,600,000 1,500,000 1,400,000 1,300,000 1,200,000 1,100,000 1,000,000 900,000 800,000 700,000 600,000 600,000 400,000 300,000 200,000 100,000

Fig. 250. The Number of Subscribers' Stations Connected to the System of the Bell Telephone Companies, December 31st of Each Year

The curve permits quicker and more accurate interpretation than the vertical bars but unfortunately curves are not readily understood by as many people. Note that the date on which the telephones are recorded is here specified as December 31st instead of as January 1st. Compare Fig. 251

GRAPHIC METHODS

A FEW CAUTIONS 357

of each vertical bar so that they would appear in each case one less than the figures given. With Fig. 249 as it is, the 1908 bar shows a great increase over 1907 and the reader is quite justified in wondering how it happened that a greatly increased number of telephones were installed during a panic year. From the chart as shown the reader is not likely to realize that 1908 is getting credit for the telephones installed during 1907, which happened to be a very prosperous business year. Having the data recorded as of December 31 each year overcomes the difficulty and makes certain that no false impression can be obtained.