How is it that we see such men as Lord Palmerston growing old in harness, working on vigorously to the end?
Mainly through equanimity of temper and habitual cheerfulness.

They have educated themselves in the habit of endurance, of not being easily provoked, of bearing and forbearing, of hearing harsh and even unjust things said of them without indulging in undue resentment, and avoiding worreting, petty, and self-tormenting cares.

An intimate friend of Lord Palmerston, who observed him closely for twenty years, has said that he never saw him angry, with perhaps one exception; and that was when the ministry responsible for the calamity in Affghanistan, of which he was one, were unjustly accused by their opponents of falsehood, perjury, and wilful mutilation of public documents.
So far as can be learnt from biography, men of the greatest genius have been for the most part cheerful, contented men--not eager for reputation, money, or power--but relishing life, and keenly susceptible of enjoyment, as we find reflected in their works.

Such seem to have been Homer, Horace, Virgil, Montaigne, Shakspeare, Cervantes.

Healthy serene cheerfulness is apparent in their great creations.