Judgment in Theorizing: Rules Have Limits.
While the men who add to known truth, whether in the realm of matter or of mind, must build on acquired knowledge, they do so with common sense, by exercise of the supreme faculty of judgment. To begin with, they perceive that every force acts within limits, acts concurrently with other forces which modify its effects. Speaking of gravity Professor William James says:—“A pendulum may be deflected by a single blow and swing back. Will it swing back the more often, the more we multiply the blows? No. For if they rain upon the pendulum too fast it will not swing at all, but remain deflected in a sensibly stationary state. Increasing the cause numerically need not increase numerically the effect. Blow through a tube; you get a certain musical note; and increasing the blowing increases for a certain time the loudness of the note. Will this be true indefinitely? No; for when a certain force is reached, the note, instead of growing louder, suddenly disappears and is replaced by its higher octave. Turn on the gas slightly and light it; you get a tiny flame. Turn on more gas and the flame increases. Will this relation increase indefinitely? No, again; for at a certain moment up shoots the flame into a ragged streamer and begins to hiss.”
In a spirit as judicial Sir William Anderson has said:—“There is a tendency among the young and inexperienced to put blind faith in formulæ, forgetting that most of them are based upon premises which are not accurately reproduced in practice, and which in many cases are unable to take into account collateral disturbances, which only experience can foresee, and common sense guard against.”