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.
