The essay previously referred to, on the "Agency of Feelings in the Formation of Habits," which appeared in the _Repository_ for February and March, 1829, was Harriet Martineau's first marked work. It was followed up by a series, commencing in the August of the same year, of "Essays on the Art of Thinking," which were continued in the magazine until December, when two chapters were given in the one number, in order, as the editor remarked, that his readers "might possess entire in one volume this valuable manual of the Art of Thought." "V," the writer of these articles, was supposed to be of the superior sex. In those days, Mr. Fox would have shown rare courage if he had informed his readers that they were "receiving valuable instruction" in how to exercise their ratiocinative faculties from the pen of a woman. In the Index, I find the references run--"V.'s" "Ode to Religious Liberty"; _his_ "Last Tree of the Forest"; _his_ "Essays on the Art of Thinking," etc., etc. The "Essays on the Art of Thinking" are nothing less than an outline of Logic. In substance, they present no great originality; but they display full internal evidence that the thoughts presented were the writer's own, and not merely copied from authority. It is really no light test of clearness and depth of thought to write on an abstruse science in lucid, perspicuous fashion, giving a brief but complete view of all its parts in their true relations. Only an accurate thinker, with a mind both capacious and orderly, can perform such a task. The highest function of the human mind is, doubtless, that of the discoverer. The original thinker, he who observes his facts from nature at first hand, who compares them, and reasons about them, and combines them, and generalizes a principle from them, is the one whom posterity to all time must honor and reverence for his additions to the store of human knowledge. But not far inferior in power, and equal in immediate usefulness, is the disciple who can judge the originator's work, and, finding it perfectly in accordance with facts as known to him, can receive it into his mind, arrange it in order, deck it with illustration, illuminate it with power of language, and represent it in a form suitable for general comprehension. There is originality of mind needed for such work; that which is done, the adaptation of the truths to be received to the receptive powers of the multitude, is an original work performed upon the truths, hardly inferior in difficulty and utility to that of him who first discerns them. This was the class of work which Harriet Martineau was beginning to do, and to do well. But there was more than this in her purposes.