“This, as a method of recording and comparing experiments, is quite convenient; but it is even more useful. The location of from three to ten points permits the experimenter to deduce accurately what would have been the results of other accurately-performed experiments under similar conditions. Whether the line is a straight one, or an hyperbola, or one expressed by some algebraical equation, the mean can be known from the extremes or one of the extremes deduced from the other extreme and the mean. In other words, _in this principle lies the key to prophecy_. For, given a mode of expressing social conditions, legal enactments, human emotions, extending through a sufficient period, and known with sufficient accuracy to be properly charted, _the present may be made to throw light upon a past too dim, and past and present point with unerring finger to the future, be it near or distant_. “When Byron wrote ‘The best of prophets of the future is the past,’ he ‘builded better than he knew.’ “But that the scientific seer may surely venture on the task of piercing the fogs which screen the past from our curious eyes, or of lifting the veils which hide the future from our anxious gaze, the simple squares and lines of the engineer must be so developed and supplemented as to represent more than two sets of conditions at once. They must show simultaneously several influences which are silently making history. It is to the enlarged application of the principle of graphical representation, that the last ten years of a life, formerly spent in the accumulation and classification of recorded knowledge, have been devoted. How well I have succeeded, I shall shortly show you. But first I must tell you by what means I have triumphed over oblivion and set upon myself the crown of prophecy. “In these charts and relief maps, horizontal distance represents time; vertical distance, space, or sections of country. Red, yellow, blue and black lines permit recording four social or other conditions at once, while elevation and degree of roughness of surface add two more to the number simultaneously expressible.