For the sake of those who are not disposed to undertake the labour of following with mathematical accuracy all the steps of the demonstrations on which the doctrines of the mechanical sciences are founded, I shall endeavour to avoid in the whole of this course of lectures every intricacy which might be perplexing to a beginner, and every argument which is fitter for the closet than for a public theatre. Here I propose to support the same propositions by experimental proofs, not that I consider such proofs as the most conclusive, or as more interesting to a truly philosophic mind, than a deduction from general principles, but because there is a satisfaction in discovering the coincidence of theories with visible effects, and because objects of sense are of advantage in assisting the imagination to comprehend, and the memory to retain, what in a more abstracted form might fail to excite sufficient attention. With regard to the mode of delivering these lectures, I shall in general entreat my audience to pardon the formality of a written discourse in favour of the advantage of a superior degree of order and perspicuity. It would unquestionably be desirable that every syllable advanced should be rendered perfectly easy and comprehensible even to the most uninformed, that the most inattentive might find sufficient variety and entertainment in what is submitted to them to excite their curiosity, and that in all cases the pleasing, and sometimes even the surprising, should be united with the instructive and the important. But, whenever there appears to be a real impossibility of reconciling these various objects, I shall esteem it better to seek for substantial utility than temporary amusement; for if we fail of being useful, for want of being sufficiently popular, we remain at least respectable; but if we are unsuccessful in our attempts to amuse, we immediately appear trifling and contemptible. It shall, however, at all times be my endeavour to avoid each extreme, and I trust that I shall then only be condemned when I am found abstruse from ostentation or uninteresting from supineness. The most difficult thing for a teacher is to recollect how much it cost himself to learn, and to accommodate his instruction to the apprehension of the uninformed. By bearing in mind this observation I hope to be able to render my lectures more and more intelligible and familiar, not by passing over difficulties, but by endeavouring to facilitate the task of overcoming them; and if at any time I appear to have failed in this attempt, I shall think myself honoured by any subsequent inquiries that my audience may be disposed to make.