Page:Popular Science Monthly Volume 85.djvu/565

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within its percentile group. Aside from the height and weight curves in 1890 for Dr. Weiner's four boys, no long series of curves have been available in scientific literature. Taking at random 170 individuals and plotting their curves for height, weight and lung capacity, we have 510 such curves for comparison.

In carrying out comparisons graphically among forms so dissimilar in absolute size as those of height, body weight and lung capacity, it was thought best to use the following units. In the height and weight curves the same base line division of 20 millimeters equals 12 months in age, while for the ordinates or vertical lines 40 millimeters equal 20 centimeters in height and 10 millimeters represent 20 pounds in weight. In the lung capacity charts a base line division of 15 millimeters is used for 12 months in age, and in the vertical or ordinates 10 millimeters represent 20 cubic inches in lung capacity. The original charts have been reduced in size and the millimeter lines taken out. The black lines represent distances of 20 millimeters on the height and weight charts and 15 and 10 millimeters on the lung capacity charts. The same Arabic numerals in a chart refer to the same individual.

Short children do not become tall, neither do tall children become short, under normal conditions. The per cent, of increase in height increments over the initial heights for a given chronological age from 6 to 18 is so comparatively uniform for each normal individual that the growth curves enable us to prophesy with considerable accuracy how tall a child of normal growth should be at any subsequent age within the