"It was owing, too, as I believe, to the ever-wakeful, intense, and ardent action of the mind, as well as the collateral meditation and study with which he had read, that his memory appeared to have possessed a faculty of discriminating among the subjects offered to its retention, and rejecting the incumbrance of what was worthless, to have seized and holden with indissoluble tenacity everything that was useful, _together with all its roots and ramifications_. He seems to have examined the historical incidents with which he had met, with all that 'large, sound, round-about sense,' as Mr. Locke calls it, which was necessary to combine with it all its causes and consequences, and render it practically useful to the purposes of life. I was several times struck with the superior advantages which he derived from these details of relative and antecedent with which he had recorded in his memory historical facts. His fellow-students were acquainted with all the prominent incidents of history; but not having examined them in all their bearings, as they had read, and impressed them, _with all their relations of cause and effect_, on their minds, it turned out that they frequently attempted to borrow aid from historical incidents, which Sidney, from his more intimate knowledge and mastery of the subjects, was able to seize and drive back upon them like routed elephants upon their own army.
"He surpassed them, too, in those powers which are derived from mathematical study; the power of keeping continually in the mind's eye, without winking or wavering, the distant proposition which is to be proven; of advancing to it by steady steps on the shortest route; and bearing up, with the strength of Atlas, the most extended and ponderous chain of logical deductions. Such was the habitual steadiness and strength of his mind, that, unlike his fellow-students, I never saw him lose sight, for an instant, of the point in debate, much less shift that point to something else; in advancing to it, I never saw him take one devious step; nor did I ever see him at any moment oppressed or entangled by the concatenation of his argument, or indicate even that he was at all sensible of its weight.
"That there may have been something in the original organization of his mind or temperament of his character, that qualified him, in a preëminent degree, for cool, dispassionate, profound, and vigorous exertion, I will not take upon me to deny; but that he owed much more of his excellence to that secret and persevering labor to which he had so nobly submitted, and by which he had given additional tone and power to his mind itself, I am perfectly convinced. His mind did, now, indeed, appear in itself the superior one; it had such a power of compression and expansion, of versatility and strength, that it seemed capable of anything and everything that he pleased. It was astonishing with what rapidity and effect he would shift the color, shape, and attitude of the same object as the emergencies of his argument required. With what closeness and unanswerable cogency he would maintain truth! and with what illusion and almost irrefutable sophistry he would disguise and metamorphose error! At the first sound of the trumpet he could draw a larger body of forces into the field in favor of an erroneous position than his adversaries could in favor of a correct one; and even when on the wrong side, which he seemed just as willing to be as he was to be on the right, he was generally astute enough to drive his adversaries into straits and keep the field himself in token of victory. Indeed the spirit of enterprise and the consciousness of his strength led him generally to prefer the wrong side to the right, and to support error with more vivacity and appearance of enjoyment than he did truth. His fault seemed to consist in the abuse of his strength; in that laxity of colloquial morals (if I may use the phrase) of which I have, just spoken, and which led him to triumph, with equal pleasure, in every victory, right or wrong.