The percentage for foreign vessels can also be read for any decade by using the reversed scale, in which zero is placed at the top and 100 per cent at the bottom. Though a double scale is scarcely necessary on a chart as simple as Fig. 126, it is frequently desirable to have a double scale.

Another very striking wall chart is shown in Fig. 127. Here as in Fig. 125 the chart was framed, but the frame shows in the photograph only as a black border. In making up this chart co-ordinate

GRAPHIC METHODS

paper was used for a background. The upper half of the chart shows the 24 hours of the day divided between hours of darkness, hours of twihght and cloudiness, and hours of sunshine, totaling 100 per cent for each month in the year. The hours of darkness are definitely known from almanac figures and can be plotted as a smooth curve.

New York Edison Company

Fig. 127. Industrial Accidents in Different Months of the Year Compared with the Hours of Stmlight Each Day in Different Months According to Weather Records for New York City in 1 9 1 o

Twenty-four hours in a day are shcmi as 100 per cent divided between darkness, semi-darkness, and sunshine. Curves showing accidents for three different years liave the same general shape as tlie upper curve representing hours of darkness. The scale for the accident curves should have been started so as to show zero at the bottom of the curve field