Now, it would be an error to say that science does not, when it can, apply to these various theories its ordinary methods of verification. They are in a different position from inevitable beliefs, which can hardly be verified because the process of verification assumes them. Yet they must not be confounded with ordinary scientific hypotheses, for they are something more and something different. Like these, they are guesses, but they are guesses directed, not by the immediate suggestion of particular experiences (which indeed they sometimes contradict), but by general tendencies which are enduring though sometimes feeble. Those who make them do not attempt the interrogation of Nature wholly free from certain forms of bias. In cross-examining that most stubborn and recalcitrant of witnesses they never hesitate to ply her with leading questions; and, whether this procedure be logically defensible or not, no lover of truth need regret its results. Readers of M. Bergson’s “Creative Evolution” may remember the picture he draws of the _élan vital_—the principle of life—forcing its way along different paths of organic evolution, some without issue or promise of progress; others leading on through regions hitherto untraversed to ends remote and unforeseen. The secular movements of science, as I conceive them, somewhat resemble this process, even though it be faintly and at a distance. There is in both a striving towards some imperfectly foreshadowed end; and in both the advance is irregular, tentative, precarious, with many changes of direction, and some reversals. Yet I would not press the parallel over-far or plunge too deeply into metaphor. It is enough to say that as, according to M. Bergson, the course followed by organic evolution cannot be wholly due to Selection, so the course followed by scientific discovery, as I read its history, cannot be wholly due to reasoning and experience. In both cases we seem forced to assume something in the nature of a directing influence, and (as I should add, though perhaps M. Bergson would not) of supramundane design. And if “a Power that makes for truth” be required to justify our scientific faith, we must surely count ourselves as theists. NOTE _Extracts from a letter from Sir Oliver Lodge on certain passages in this lecture relating to Energy and its transformations._ * * * * * You say, on page 226, “Energy, we are taught, is of two kinds: kinetic and potential energy—energy in act and energy in possibility.”