On Monday, December 22, at two, he gave the introduction to a course of four lectures on Mechanics and Physics. In this lecture he dwelt on the objects of natural philosophy, division of the science, utility of the study, plan of the lectures. The second lecture was on Monday, 26, at eight P.M., on the Properties of Matter; extension, impenetrability, divisibility, inertia, various species of attraction and repulsion, _motion_, _forces_, composition of forces, _collision_, _pendulums_. The third lecture was on Wednesday, 28, at two. _Projectiles_; resistance of the air, _mechanic powers_, strength of timber. The fourth on Thursday, at two. Pneumatics; nature of electric fluids, the atmosphere, air-pump, spring and weight of the air proved by experiments, barometer. The last lecture was given on Saturday, 31, at eight. This was followed by other courses, making altogether twenty lectures. After his return to Manchester Dalton wrote to his brother, February 1, 1804: DEAR BROTHER,--I have the satisfaction to inform thee that I returned safe from my London journey last seventh day, having been absent six weeks. It has on many accounts been an interesting _vocation_ to me, though a very laborious one. I went in a great measure unprepared, not knowing the nature and manner of the lectures at the Institution nor the apparatus. My first was on Thursday, December 22, which was introductory, being entirely written, giving an account of what was intended to be done; and on natural philosophy in general. All lectures were to be one hour each, or as nearly as might be. The number attending were from one to three hundred of both sexes, usually more than half men. I was agreeably disappointed to find so _learned_ and _attentive_ an audience, though many of them of rank. It required great labour on my part to get acquainted with the apparatus and to draw up the order of experiments and repeat them in the intervals between the lectures, though I had one pretty expert to assist me. We had the good fortune, however, never to fail in any experiment, though I was once so ill prepared as to beg the indulgence of the audience as to part of the lecture, which they most handsomely and immediately granted me by a general plaudit. The scientific part of the audience was wonderfully taken with some of my original notions relative to heat, the gases &c., some of which had not before been published. Had my hearers been generally of the description I had apprehended, the most interesting lectures I had to give would have been the least relished; but, as it happened, the expectation formed had drawn several gentlemen of first-rate talents together, and my eighteenth, on Heat and the Laws of Expansion, &c., was received with the greatest applause; with very few experiments. The one that followed was on _Mixed Elastic Fluids_, in which