With Keely's claim, that latent force exists in all forms of matter, it is different; for it is susceptible of proof by experiment. In the days when the sphericity of the earth was denied, for the asserted reason that the waters of the oceans and seas on its surface would be thrown off in its revolutions were it so, because water could not stay on a round ball, the statement could not be disputed; the theory of the laws of gravitation being then unknown. Copernicus and Galileo had nothing but theories to offer; consequently it took long years to overcome the bigotry and the baneful influence of the great authorities of the time. It is otherwise with Keely, who, for fifteen years and more, has been demonstrating this discovery to thousands of men; some of whom, but not all, were competent to form an opinion as to whether he was "humbugging with compressed air," or with a concealed dynamo, or, still more absurd, with tricks in suction, as I asserted by a learned professor. Now that some of our men of science have consented to form their opinions from observation, without interfering with the lines of progressive experimental research which the discoverer is pursuing, there seems to be no doubt as to the result; nor of the protection of the discovery by science. Truth is mighty, and must in the end prevail over mere authority. It has been said that we need nothing more than the history of astronomy to teach us how obstinately the strongholds of error are clung to by incompetent reasoners; but when a stronghold is demolished, there is nothing left to cling to. Sir John Lubbock says:--The great lesson which science teaches is how little we yet know, and how much we have still to learn. To which it might be added, and how much we have to unlearn!