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Rh barometer, the rising of the balloon, and a multitude of other things with which at first sight it has no connection at all. This is another instance of the synthetic or assimilative phase of scientific thinking.

If we revert to the advantages of scientific over empirical thinking, we find that we now have the clue to them.

(a) The increased security, the added factor of certainty or proof, is due to the substitution of the detailed and specific fact of atmospheric pressure for the gross and total and relatively miscellaneous fact of suction. The latter is complex, and its complexity is due to many unknown and unspecified factors; hence, any statement about it is more or less random, and likely to be defeated by any unforeseen variation of circumstances. Comparatively, at least, the minute and detailed fact of air pressure is a measurable and definite fact—one that can be picked out and managed with assurance.

(b) As analysis accounts for the added certainty, so synthesis accounts for ability to cope with the novel and variable. Weight is a much commoner fact than atmospheric weight, and this in turn is a much commoner fact than the workings of the suction pump. To be able to substitute the common and frequent fact for that which is relatively rare and peculiar is to reduce the seemingly novel and exceptional to cases of a general and familiar principle, and thus to bring them under control for interpretation and prediction.

As Professor James says: "Think of heat as motion and whatever is true of motion will be true of heat; but we have a hundred experiences of motion for every one of heat. Think of rays passing through this lens as cases of bending toward the perpendicular, and you