The Bank reserve then never ought to be diminished below the 'apprehension point.' And this is as much as to say, that it never ought very closely to approach that point; since, if it gets very near, some accident may easily bring it down to that point and cause the evil that is feared.
There is no 'royal road' to the amount of the 'apprehension minimum': no abstract argument, and no mathematical computation will teach it to us.

And we cannot expect that they should.

Credit is an opinion generated by circumstances and varying with those circumstances.

The state of credit at any particular time is a matter of fact only to be ascertained like other matters of fact; it can only be known by trial and inquiry.

And in the same way, nothing but experience can tell us what amount of 'reserve' will create a diffused confidence; on such a subject there is no way of arriving at a just conclusion except by incessantly watching the public mind, and seeing at each juncture how it is affected.
Of course in such a matter the cardinal rule to be observed is, that errors of excess are innocuous but errors of defect are destructive.
Too much reserve only means a small loss of profit, but too small a reserve may mean 'ruin.' Credit may be at once shaken, and if some terrifying accident happen to supervene, there may be a run on the Banking department that may be too much for it, as in 1857 and 1866, and may make it unable to pay its way without assistance--as it was m those years.
And the observance of this maxim is the more necessary because the 'apprehension minimum' is not always the same.