The next letter to Abbott, dated April 9, recounts an explosion in which both he and Sir Humphry Davy received considerable injury. In June he wrote to Abbott four very remarkable letters concerning lectures and lecturers. He had already heard Tatum and Davy, and had now assisted Brande and Powell in their lectures, and had keenly observed their habits, peculiarities, and defects, as well as the effects they produced on the audience. He writes without the slightest suspicion of suggestion that he himself has any likelihood of becoming a lecturer, and says that he does not pretend to any of the requisites for such an office. “If I am unfit for it,” he says, “’tis evident that I have yet to learn; and how learn better than by the observation of others? If we never judge at all, we shall never judge right.” “I, too, have inducements in the C[ity] P[hilosophical] S[ociety] to draw me forward in the acquisition of a small portion of knowledge on this point.” “I shall point out but few beauties or few faults that I have not witnessed in the presence of a numerous assembly.” He begins by considering the proper shape of a lecture-room; its proper ventilation, and need of suitable entrances and exits. Then he goes on to consider suitability of subjects and dignity of subject. In the second of the letters he contrasts the perceptive powers of the eye and ear, and the proper arrangements for a lecturer’s table; then considers diagrams and illustrations. The third letter deals with the delivery and style of the lecture, the manner and attitudes of the lecturer, his methods of keeping alive the attention of the audience, and duration of the discourse. In the fourth of these letters (see p. 228), he dwells on the mistakes and defects of lecturers, their unnecessary apologies, the choice of apt experiments, and avoidance of trivialities. [Sidenote: PROPOSALS FOR FOREIGN TRAVEL.] In September, 1813, after but six months of work in the laboratory, a proposition came to him from Sir Humphry Davy which resulted in a complete change of scene. It was an episode of foreign travel, lasting, as it proved, eighteen months. In the autobiographical notes he wrote:-- In the autumn Sir H. Davy proposed going abroad, and offered me the opportunity of going with him as his amanuensis, and the promise of resuming my situation in the Institution upon my return to England. Whereupon I accepted the offer, left the Institution on October 13, and, after being with Sir H. Davy in France, Italy, Switzerland, the Tyrol, Geneva, &c., in that and the following year, returned to England and London April 23, 1815. Before he left England, on September 18, 1813, at the request of his mother, he wrote to an uncle and aunt the following account of himself:--