Page:Popular Science Monthly Volume 59.djvu/463

Rh interpretation is still to be worked out. The beginnings are, however, instructive.

Variation polygons are of two main sorts—simple and complex. Simple variation polygons possess only a single mode, whilst complex

polygons usually show a trace of more than one mode. Simple variation polygons are of several types. Some are symmetrical about the mode as in Fig. 5. Others are more or less unsynmetrical or skew, as

they are technically called (Fig. 6). Skew polygons usually tail out at the base further from the mode on one side than on the other. The polygon is said to be skew in the direction of this longer partial base. Why some distributions are symmetrical and others skew is not fully