Page:Graphic methods for presenting facts (1914).djvu/149

 the standard of living has very greatly changed in the period of time from 1895 to 1912. Prices in recent years might be expected to be considerably higher than in the earlier years, without any regard to the size of the apple crop. Besides this, numerous diseases have affected apple trees in recent years, requiring more care than formerly to produce good fruit. This would also have some tendency to raise prices in spite of the tremendous number of apple trees which have come into bearing in the later portion of the period of time under consideration. The general method of plotting shown in Fig. 119 is of great importance and it should be kept in mind whenever two curves are found having similarities such as are seen in Fig. 118. Other examples of this method of plotting to study the correlation of two related subjects will be found in the last portion of Chapter X.

Fig. 119. The Average Price of Apples in the United States as Compared with the Total Supply

By this method, the positions of the dots on the chart show whether there is any close relation between supply and price. The dots fall in fairly regular order, proving better than Fig. 118 that the price does largely depend upon the supply. A smooth curve has been drawn to represent approximately the general relation between supply and price which the dots might seem to indicate. Note that the year is stated for each dot shown

Fig. 120 contains much information for the student of history. We are here interested particularly in the record of the United States. That curve line has accordingly been made much heavier than any of the others, so that it may be brought prominently to the eye of the reader. By visually projecting the curves for Russia and the United States beyond the limits of the chart, it appears that we should equal Russia's population within the next few decades. It must be remembered in viewing this chart that the populations of the Asiatic countries (especially the populations of China and India) are not shown here. If all the countries of the world were considered, it would be seen at once that for many years to come there is no likelihood of the United States having the greatest population in the world. It is only because Asiatic countries have been omitted that we seem to be so nearly the head of the list.