The Unseen World and Other Essays

The more-crude theories of early times are to be chiefly distinguished from the less-crude theories of to-day as being largely the products of random guesswork. Hypothesis, or guesswork, indeed, lies at the foundation of all scientific knowledge. The riddle of the universe, like less important riddles, is unravelled only by approximative trials, and the most brilliant discoverers have usually been the bravest guessers. Kepler's laws were the result of indefatigable guessing, and so, in a somewhat different sense, was the wave-theory of light. But the guesswork of scientific inquirers is very different now from what it was in older times. In the first place, we have slowly learned that a guess must be verified before it can be accepted as a sound theory; and, secondly, so many truths have been established beyond contravention, that the latitude for hypothesis is much less than it once was. Nine tenths of the guesses which might have occurred to a mediaeval philosopher would now be ruled out as inadmissi