It is certain that the prices (that of pine lumber, for instance, shown by the upper curve) did not have the uniform rate of increase which the straight hue from 1897 to 1907 would indicate. We are considering here, however, the changes over the period as a whole, and we can for simplicity draw a straight line and neglect all the fluctuations of intervening years. The general scheme of Fig. 53 is convenient, as the neglect of detail brings the main information out clearly. Fig. 53 has, unfortunately, been drawn

in a misleading manner in that the reader is

likely to interpret the cm-ves as if zero were shown at the bottom of the chart. The general rule in charts of this kind is that zero should be shown as the bottom line, or, if not shown at the bottom, that the omission of zero should be clearly indicated. As Fig. 53 is shown on a percentage basis, the 100 per cent line should be clearly indicated by drawing a broad line on the chart for the line opposite the figure 100 in the scale. It would have been better, perhaps, to have plotted the data so that zero would replace the figure 100. On a scale so made, pine lumber would go up 83 per cent, while railroad rates would be shown

American Review of Revieu-s

Fig. 52. The Increasing Number of Students in the Co-operative Course of the Engineering College of the University of Cinciruiati

This illustration was originally used as a companion piece to the chart of Fig. 51. For a popular exhibit the use of vertical bars brings out information quite clearly. Though curves (such as are shown in later chapters) are superior to vertical bars, it is imfortunately true that most people do not know how to read even the simplest curves correctly.