The moral basis of the intellectual life appears to be the idea of discipline; but the discipline is of a very peculiar kind, and varies with every individual. People of original power have to discover the original discipline that they need. They pass their lives in thoughtfully altering this private rule of conduct as their needs alter, as the legislature of a progressive State makes unceasing alterations in its laws. When we look back upon the years that are gone, this is our bitterest regret, that whilst the precious time, the irrecoverable, was passing by so rapidly, we were intellectually too undisciplined to make the best personal use of all the opportunities that it brought. Those men may be truly esteemed happy and fortunate who can say to themselves in the evening of their days--"I had so prepared myself for every successive enterprise, that when the time came for it to be carried into execution my training ensured success." I had thought of some examples, and there are several great men who have left us noble examples of self-discipline; but, in the range and completeness of that discipline, in the foresight to discern what would be wanted, in the humility to perceive that it was wanting, in the resolution that it should _not_ be wanting when the time came that such knowledge or faculty should be called for, one colossal figure so far excels all others that I cannot write down their names with that of Alexander Humboldt. The world sees the intellectual greatness of such a man, but does not see the substantial moral basis on which the towering structure rose. When I think of his noble dissatisfaction with what he knew; his ceaseless eagerness to know more, and know it better; of the rare combination of teachableness that despised no help (for he accepted without jealousy the aid of everybody who could assist him), with self-reliance that kept him always calm and observant in the midst of personal danger, I know not which is the more magnificent spectacle, the splendor of intellectual light, or the beauty and solidity of the moral constitution that sustained it. LETTER III. TO A FRIEND WHO SUGGESTED THE SPECULATION "WHICH OF THE MORAL VIRTUES WAS MOST ESSENTIAL TO THE INTELLECTUAL LIFE." The most essential virtue is disinterestedness--The other virtues possessed by the opponents of intellectual liberty--The Ultramontane party--Difficulty of thinking disinterestedly even about the affairs of another nation--English newspapers do not write disinterestedly about foreign affairs--Difficulty of disinterestedness in recent history--Poets and their readers feel it--Fine subjects for poetry in recent events not yet available--Even history of past times rarely disinterested--Advantages of the study of the dead languages in this respect--Physicians do not trust their own judgment about their personal health--The virtue consists in endeavoring to be disinterested.