thoughts about him, and his mind clear and free for the contemplation and description of his subject. His action should not be hasty and violent, but slow, easy, and natural, consisting principally in changes of the posture of the body, in order to avoid the air of stiffness or sameness that would otherwise be unavoidable. His whole behaviour should evince respect for his audience, and he should in no case forget that he is in their presence." He allows a lecturer to prepare his discourse in writing, but not to read it before the audience, and points out how necessary it is "to raise their interest at the commencement of the lecture, and by a series of imperceptible gradations, unnoticed by the company, keep it alive as long as the subject demands it." This of course forbids breaks in the argument, or digressions foreign to the main purpose, and limits the length of the lecture to a period during which the listeners can pay unwearied attention. He castigates those speakers who descend so low as "to angle for claps," or who throw out hints for commendation, and shows that apologies should be made as seldom as possible. Experiments should be to the point, clear, and easily understood: "they should rather approach to simplicity, and explain the established principles of the subject, than be elaborate and apply to minute phenomena only.... 'Tis well, too, when the lecturer has the ready wit and the presence of mind to turn any casual circumstance to an illustration of his subject." But experiments should be explained by a satisfactory theory; or if the scientific world is divided in opinion, both sides of the question ought to be stated with the strongest arguments for each, that justice may be done and honour satisfied.