Page:Graphic methods for presenting facts (1914).djvu/113

 that the chart has been drawn in too optimistic a manner because it does not show zero at the bottom of the scale. It would have given a much more conservative impression if the excellent record of circulation growth had been plotted in curves having the zero line shown at the bottom of the chart, so that the relative growth could be accurately judged visually.

In Fig. 89 a large amount of information has been condensed into a small amount of space, yet the chart is fairly clear and easy of interpretation. Several ingenious combinations have been included as, for instance, the arrows that show the prevailing direction of the wind each day. The chart gives unusually complete information in a most convenient form for any ventilating engineer or power-plant manager who wishes to keep careful track of his cost of coal in different months of the year as dependent upon weather conditions.

Heating and Ventilating Magazine

Fig. 89. Record of the Weather in New York City for December, 1912

The heavy line indicates temperature in degrees Fahrenheit

The light solid line shows wind velocity in miles per hour

The dotted line depicts relative humidity in percentage from readings taken at 8 a.m. and 8 p.m.

Arrows portray the prevailing direction of the wind

Initials at the base of the chart show weather conditions as follows: S, clear; PC, partly cloudy; C, Cloudy; R, rain; Sn, snow

Fig. 90 shows an example of double co-ordinate ruling on the same sheet of paper. The scheme of using double co-ordinates is not very well known even to engineers and it seems worthy of attention here. The solid line plotted in the general form of a curve with a flat space for each month shows the total water consumption in millions of gallons per day. The total water consumption is read from the scale of the horizontal lines as for any curve plotted by rectangular co-ordinates. The slanting lines are drawn after the total