278 THE MISMEASURE OF MANSuch systems of high positive correlation are found frequently
in nature. In my own first study in factor analysis, for example, I
considered fourteen measurements on the bones of twenty-two
species of pelycosaurian reptiles (the fossil beasts with the sails on
their backs, often confused with dinosaurs, but actually the ances-
tors of mammals). My first principal component resolved 97.1 per-6 • 4 Geometric representation of correlations among eight tests when all
correlation coefficients are high and positive. The first principal compo-
nent, labeled 1, lies close to all the vectors, while the second principal com-
ponent, labeled 2, lies at right angles to the first and does not explain much
information in the vectors.