We have not only Faraday's discoveries, but those of Scheele, the Swedish chemist, as an example of exact observations leading to erroneous conclusions. The investigations of Scheele led up to the rich harvest which has since been reaped from a knowledge of the nature of the compounds of organic chemistry. Scheele was one of the founders of quantitative analysis, but the phlogistic theory advanced by him was overthrown--the fate of all theories which are not based on solid foundations. Faraday admitted that his own ideas on gravitating force, and of the ether, were but vague impressions of his mind thrown out as matter for speculation. He left no theory on these lines, for he had nothing to offer as the result of demonstration, nor even of sufficient consideration to broach a theory: merely impressions, which are allowable for a time as guides to thought and farther research. Yet more than once did these speculations of his giant intellect touch upon one of nature's hidden laws, the greatest one yet made known to man. Had Faraday lived long enough to pursue his researches, from his starting point of conjecture, he would have been, without doubt, instead of Keely, the discoverer of the latent or hidden potencies existing in all forms of matter, visible and invisible. But the physicists of his time looked upon his speculations as contrary to the received dogmas of science, and preferred their own errors to his speculations. They saw the signpost, but took the road directly opposite to the one Faraday had pointed out. It is admitted that even a false theory, when rightly constructed, has its uses, and that, instead of hindering, it hastens the advance of knowledge. Every one, possessing the slightest acquaintance with the history of astronomy, knows that the doctrines of cycles, epicycles and ellipses, were begotten naturally and necessarily out of each other; and that if Kepler had not propounded speculative errors Newton would not have hit upon speculative truth. It has been said that when men of science disclaim hypotheses, or speculation, they are either unfit for their vocation or, like Newton, they are better than their creed. Hypotheses are at once the effect and the cause of progress. One might as well attempt to preserve and employ an army without organization as to preserve and employ phenomena without a theory to weld them into one. But the theory must be provisionally, if not positively, true; it must be intelligible and consistent; it must explain a greater number of facts and reconcile a greater variety of apparent contradictions than any which has preceded it; and it must have become developed not by the addition merely, but by the addition and solution, of subsidiary explanations. I ask of you an examination of Keely's theories before giving an opinion of them.