Page:The Harveian oration 1866.djvu/21

 ague with cinchona bark, but how far are we still from understanding in any scientific sense the specific action by which the cure is effected.

This practical utilization of facts before their real nature has been scientifically determined is not peculiar to medicine. It may be observed in all the arts which nearly concern men's daily welfare and interests. The exigencies of society, the wants or sufferings of some men, the cupidity or ambition of others, are parents of invention far more prolific than the pure love of science.

The rotation of crops was practised by farmers long before botanists could give any reasonable explanation of its advantages. Thus art anticipates science. In mechanics, practice almost invariably precedes theory, and often by very long periods. 'Tis but a few years since Dr Joule determined the thermal equivalent for mechanical work. For ages upon ages the fact had been utilized by savages, when they rubbed together two dry sticks to procure fire. Suction-pumps had been at work for hundreds of years before Torricelli showed the true cause of the suction. The boomerang is used by Australian savages, the screw-propeller moves the navies of great nations,