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488 must also be considered as realising its purposes through physical causes, as, says the Greek philosopher, "Nature does nothing in vain."

Aristotle so far recognised the value of experiment, but Bacon much more so. "And so to meet these evils we, with much and faithful service, have sought out and gathered helps for the Senses from every side; so to supply substitutions where they fail, rectifications where they vary. Nor do we attempt this with Instruments so much as with Experiments. For their subtilty is far greater than that of the Senses, even when aided by exquisite instruments. And so we do not allow much to the immediate and proper perception of the Senses; but make the Senses judge only of Experiments, Experiments of things." Consider also Bacon's Experientia Literata. It is largely Bacon's clear recognition of the value of experiment which makes his philosophy of discovery a distinct advance on that of Aristotle. The progress of natural science depends upon experiment more than upon any other factor. Aristotle observed more than experimented, Bacon did both. Experiment always works under hypothesis. A scientist experiments so as to prove or disprove theory. Now Aristotle implicitly recognised hypothesis but had no adequate appreciation of the necessity for verification, and consequently of the necessity for experiment. Bacon recognised hypothesis (most clearly, no doubt, as outside his formal method). But such was that method's fidelity to fact and avoidance of any kind of 'anticipatio mentis,' that once Bacon had in any way recognised hypothesis as an aid to discovery, he could not have carried inconsistency so far as to neglect verification. So Bacon recognises experiment also.

It is true that in practice Bacon sometimes fails to experiment where experiment was necessary. Thus, experiments with the air thermometer, which he mentions in the Novum Organum, would have shown him the absurdity of the old theory, to which, like Aristotle, he still clings, that some things are naturally hot