“In my early life I set about the task of reconciling these discrepancies by converging lines of testimony; and so satisfactory were the results, so unerringly was each cause deduced from its many effects, that I conceived the idea of not only reconciling historical discrepancies as to occurrences and motives, but reading the future by continuing each chain of reasoning into the time to come. In other words, if by my inductive method, more light is thrown on the occurrences in Babylon, Media, Lydia, Egypt, twenty-five centuries ago, than by the non-inductive method, upon those at Shiloh, but twenty-five years past, it should be safer to predict by it the outcomings of the next generation, than by the usual methods, those of the next spring or summer. I deemed that ‘by labor and intent study (which I take to be my portion in this life) joined with the strong propensity of nature, I might perhaps leave something so written to after times, that they should not willingly let it die.’ Each year that I continued my studies, which embraced not only the collection and assimilation of facts, but their classification and the formation of deductions therefrom, the more firmly I become impressed with the idea of turning the electric light of induction along the path of prophecy, rather than merely illuminating therewith the fogs of history. “‘I, thus neglecting worldly ends, all dedicated To closeness, and the bettering of my mind,’ set about this problem. Ample means, an excellent constitution, and correct and regular habits, have enabled me to accomplish during the past fifty years--for through so long a time have I been striving for my object--much more than is given to most men to do, and more even than I had given myself reason to expect or hope. We now stand in ‘this narrow isthmus ’twixt two boundless seas, the past, the future, two eternities.’ I HAVE EXPLORED THEM BOTH. “But I detect in your manner an impatience which I cannot condemn, and shall plunge at once into an explanation of my methods, leaving until later a statement of what I have been able to accomplish thereby. “It has long been the custom of professional engineers to represent graphically on sheets of paper ruled in squares, various properties of matter under regularly-varying conditions. For instance, to show the electric conductivity of wire at various temperatures, horizontal strips represent degrees of temperature, and vertical strips, degrees of conductivity; and if a line connecting points corresponding to conductivity at various temperatures be convexly curved above, it shows that conductivity decreases more rapidly than temperature increases. If the line be straight, it shows that conductivity decreases in the same ratio as temperature increases. The use of several colored lines, or of solid and of variously broken or dotted lines, permits comparison of the conductivity of several metals or alloys.