Page:Graphic methods for presenting facts (1914).djvu/139

 Engineering Record

Fig. 108. Comparison of Flood Rise in Two Rivers in New York State During the Floods of March, 1913

In the preceding illustrations of this chapter there has been such similarity in the shape of the curves considered that they were superimposed for comparison. Here the curves are of different shape and they are shown in separate fields so that the contrast may be more striking. The chart at the left should have had the zero line shown. It is dangerous to base conclusions on the comparison of two curves unless the zero lines are shown in each case

Iron Age

Fig. 109. Comparison of Different Kinds of Steel Containing 0.2 per cent Carbon, as shown by Tensile Tests on Specimens 100 mm. long and 13.8 mm. diameter. The Vertical Scale Represents Thousands of Pounds per Square Inch and also Percentage of Contraction or Elongation

The heavy line shows ultimate strength

The dash line shows elastic limit

The dash-dot line shows percentage contraction

The light line shows percentage elongation

In this chart the thing of greatest interest is the contrast seen by comparing the shapes of the curves for different steels. Though it is best to have curves of such distinct shape plotted in separate fields, it is ordinarily most convenient to have the fields themselves placed vertically instead of horizontally

broken off, most readers will not imagine correctly the great height to which that peak would extend if it were shown in full. The chart could have been greatly improved if the upper portion of the peak had been drawn in full size horizontally as though hinged near the upper margin of the drawing. Since the full height of the peak is