A heavy drag-weight upon the powers of some men is the uncertainty of their powers. The man has not his powers at command. His mind is a capricious thing, that works when it pleases, and will not work except when it pleases. I am not thinking now of what to many is a sad disadvantage: that nervous trepidation which cannot be reasoned away, and which often deprives them of the full use of their mental abilities just when they are most needed. It is a vast thing in a man's favor, that whatever he can do he should be able to do at any time, and to do at once. For want of coolness of mind, and that readiness which generally goes with it, many a man cannot do himself justice; and in a deliberative assembly he may be entirely beaten by some flippant person who has all his money (so to speak) in his pocket, while the other must send to the bank for his. How many people can think next day, or even a few minutes after, of the precise thing they ought to have said, but which would not come at the time! But very frequently the thing is of no value, unless it come at the time when it is wanted. Coming next day, it is like the offer of a thick fur great-coat on a sweltering day in July. You look at the wrap, and say, "Oh, if I could but have had you on the December night when I went to London by the limited mail, and was nearly starved to death!" But it seems as if the mind must be, to a certain extent, capricious in its action. Caprice, or what looks like it, appears of necessity to go with complicated machinery, even material. The more complicated a machine is, the liker it grows to mind, in the matter of uncertainty and apparent caprice of action. The simplest machine--say a pipe for conveying water--will always act in precisely the same way. And two such pipes, if of the same dimensions, and subjected to the same pressure, will always convey the self-same quantities. But go to more advanced machines. Take two clocks or two locomotive engines, and though these are made in all respects exactly alike, they will act (I can answer at least for the locomotive engines) quite differently. One locomotive will swallow a vast quantity of water at once; another must be fed by driblets; no one can say why. One engine is a _fac-simile_ of the other; yet each has its character and its peculiarities as truly as a man has. You need to know your engine's temper before driving it, just as much as you need to know that of your horse, or that of your friend. I know, of course, there is a mechanical reason for this seeming caprice, if you could trace the reason. But not one man in a thousand could trace out the reason. And the phenomenon, as it presses itself upon us, really amounts to this: that very complicated machinery appears to have a will of its own,--appears to exercise something of the nature of choice. But there is no machine so capricious as the human mind. The great poet who wrote those beautiful verses could not do _that_ every day. A good deal more of what he writes is poor enough; and many days he could not write at all. By long habit the mind may be made capable of being put in harness daily for the humbler task of producing prose; but you cannot say, when you harness it in the morning, how far or at what rate it will run that day.