The perfection of his memory was amazing.  During the year following the survey, when we had frequent occasion to compare recollections, I observed that no circumstance of our labors was shadowy or incomplete in his memory.  He could refer to every trifling incident of the tour, recall every road and path that we had followed, every field and ledge that we had examined, particularize the day of the week on which we had dined or supped at such a tavern, and mention the name of the landlord.  I asked him how he was able to remember such minutiae.  He replied, that it was his custom, on going to bed, to call up, in the darkness and stillness, all the incidents of the day’s experience, in their proper order, and cause them to move before him like a diorama through a spiritual morning, noon, and evening.  “It has often appeared to me,” he said, “that in this purely mental process I see objects more distinctly than I behold them in the reality.”

But his memory doubtless gained an immense additional advantage from his habitual seclusion, from his unconcern with the distracting customs of society, and, most of all, from the imperturbable abstraction under which he studied and observed.  With him there was no blending of collateral subjects, no permitted intrusion of things irrelevant or trivial, so that the channels of his thoughts were always single, deep, and traceable.  It was a mental straightforwardness and conscientiousness, as rare, perhaps, as moral rectitude itself.

In diet, Percival was the most abstemious person I ever knew.  His health was uniformly good,—­the specimens of a geologist, when he collects them himself, being as favorable to digestion and appetite as the pebbles to a chicken; yet, I am persuaded, my companion in no case violated the golden rule of leaving the table unsated.  No matter how long had been his fast, he showed no impatience of hunger, made no remark upon the excellence of any dish, found fault with nothing, or, at most, only seemed to miss drinkable coffee and good bread, articles seldom to be met with in the country.  He ate slowly, selecting his food with the discrimination which ought to belong to a chemist or physiologist, and then thought no more about it.  Alcoholic drinks he never tasted, except an occasional glass of wine, to which his attention perhaps had been called on account of its age or superior excellence.  Even then it was not the flavor which interested him, so much as the history, geographical and other.

Peculiar as he was in his own habits of diet, he offered no strictures upon the practice of others, however different, unless it ran into hurtful excesses.  The maxim of Epictetus in the “Enchiridion,” “Never preach how others ought to eat, but eat you as becomes you,” seemed to be his rule.  Indeed, Percival was one of those rare men who withhold alike censure and praise respecting the minor matters of life.  Not that he was without opinions on such subjects; but, to obtain them, one was forced