Just so one can be in what I might call "efficiency-equilibrium" (neither gaining nor losing power when once the equilibrium is reached) on astonishingly different quantities of work, no matter in what direction the work may be measured. It may be physical work, intellectual work, moral work, or spiritual work. Of course there are limits: the trees don't grow into the sky. But the plain fact remains that men the world over possess amounts of resource which only very exceptional individuals push to their extremes of use. But the very same individual, pushing his energies to their extreme, may in a vast number of cases keep the pace up day after day, and find no "reaction" of a bad sort, so long as decent hygienic conditions are preserved. His more active rate of energizing does not wreck him; for the organism adapts itself, and as the rate of waste augments, augments correspondingly the rate of repair. I say the _rate_ and not the _time_ of repair. The busiest man needs no more hours of rest than the idler. Some years ago Professor Patrick, of the Iowa State University, kept three young men awake for four days and nights. When his observations on them were finished, the subjects were permitted to sleep themselves out. All awoke from this sleep completely refreshed, but the one who took longest to restore himself from his long vigil only slept one-third more time than was regular with him. If my reader will put together these two conceptions, first, that few men live at their maximum of energy, and second, that anyone may be in vital equilibrium at very different rates of energizing, he will find, I think, that a very pretty practical problem of national economy, as well as of individual ethics, opens upon his view. In rough terms, we may say that a man who energizes below his normal maximum fails by just so much to profit by his chance at life; and that a nation filled with such men is inferior to a nation run at higher pressure. The problem is, then, how can men be trained up to their most useful pitch of energy? And how can nations make such training most accessible to all their sons and daughters. This, after all, is only the general problem of education, formulated in slightly different terms. "Rough" terms, I said just now, because the words "energy" and "maximum" may easily suggest only _quantity_ to the reader's mind, whereas in measuring the human energies of which I speak, qualities as well as quantities have to be taken into account. Everyone feels that his total _power_ rises when he passes to a higher _qualitative_ level of life.