Although, for practical purposes, it is convenient to mark it out into the primary regions of Physics, Chemistry, and Biology, and to subdivide these into subordinate provinces, yet the method of investigation and the ultimate object of the physical inquirer are everywhere the same.
All physical science starts from certain postulates.
One of them is the objective existence of a material world. The justification of their employment, as axioms of physical philosophy, lies in the circumstance that expectations logically based upon them are verified, or, at any rate, not contradicted, whenever they can be tested by experience. The geocentric system of astronomy, with its eccentrics and its epicycles,, was an hypothesis utterly at variance with fact, which nevertheless did great things for the advancement of astronomical knowledge. Kepler was the wildest of guessers. It sounds paradoxical to say that the attainment of scientific truth has been effected, to a great extent, by the help of scientific errors.