describe was misunderstood. We are hardy enough to prophesy a similar career and fate for the theory of Relativity. The technical physical theory, at present imperfectly understood, will become still more vague and dim. History repeats itself, and Relativity, like Evolution, after receiving a number of intelligible but somewhat inaccurate popular expositions in its scientific aspect, will be launched on a world-conquering career. We suggest that, by that time, it will probably be called Relativismus . Many of these larger applications will doubtless be justified; some will be absurd and a considerable number will, we imagine, reduce to truisms. And the physical theory, the mere seed of this mighty growth, will become once more the purely technical concern of scientific men." [Footnote: The Times (London), Literary Supplement , June 2, 1921, p. 352. Professor Einstein said when he was in America in 1921 that people tended to overestimate the influence of his theory, and to under-estimate its certainty.]
But for such a world-conquering career an idea must correspond, however imprecisely, to something. Professor Bury shows for how long a time the idea of progress remained a speculative toy. "It is not easy," he writes, [Footnote: J. B. Bury, The Idea of Progress, p. 324.] "for a new idea of the speculative order to penetrate and inform the general consciousness of a community until it has assumed some external and concrete embodiment, or is recommended by some striking material evidence. In the case of Progress both these conditions were fulfilled (in England) in the period 1820-1850." The most striking evidence was furnished by the mechanical revolution. "Men who were born at the beginning of the century had seen, before they had passed the age of thirty, the rapid development of steam navigation, the illumination of towns and houses by gas, the opening of the first railway." In the consciousness of the average householder miracles like these formed the pattern of his belief in the perfectibility of the human race.
Tennyson, who was in philosophical matters a fairly normal person, tells us that when he went by the first train from Liverpool to Manchester