"However much men may honestly endeavour to limit the exercise of their discretion by definite rule, there must always be room for idiosyncracy; and idiosyncracy, as the word expresses, varies with the man. But there is, besides this, that of which every student of legal history must be aware, the leaning of the Courts for a certain time in a particular direction, balanced at least, if not reversed, by the leaning of the Courts for a certain time in a direction opposite. The current of legal decision runs often to a point which is felt to be beyond the bounds of sound and sane control, and there is danger sometimes that the retrocession of the current should become itself extreme."