Roget says that if we are to reason at all, we can reason only upon the principle that for every effect there must exist a corresponding cause; or, in other words, that there is an established and invariable order of sequence among the changes which take place in the universe. The bar to all further reasoning lies in the fact that there are men who, admitting all the phenomena we behold are the effects of certain causes, still say that these causes are utterly unknown to us, and that their discovery is wholly beyond the reach of our faculties. Those who urge this do not seem to be aware that its general application in every sense would shake the foundation of every kind of knowledge--even that which we regard as built upon the most solid basis. Of causation it is agreed that we know nothing; all that we do know is that one event succeeds another with undeviating constancy; and what do we know of magnetism, electricity, galvanism, but such facts as have been elicited by the labours of experimental enquirers, and the laws which have been deduced from their generalization? Would it be considered a sufficient reason for the absolute rejection of any of these facts--or a whole class of facts--that we are still ignorant of the principle upon which they depend, and that such knowledge is beyond our reach? Facts are every day believed, upon observation, or upon testimony, which we should be exceedingly puzzled to account for, if called upon to do so. Every man who has passed the mere threshold of science ought to be aware that it is quite possible to be in possession of a series of facts, long before he is capable of giving a rational and satisfactory explanation of them; in short, before he is enabled to discover their causes. Also that he must classify his facts and construct hypotheses before he can impart his experimental position to others. Many things which were, for a long time, treated as fabulous and incredible have been proved, in our age, to be authentic facts, as soon as the evidence in support of them was duly subjected to the crucible of scientific investigation. Take, for example, Professor Dewar's researches in the cause, or origin, of meteoric stones. Fortunately for his branches of research and experiment, he is possessed of that philosophical spirit and energy which enables him to divest himself of all prejudice, and, in constructing his theories, to welcome the evidence of truth from whatever quarter it approaches. More than two thousand years elapsed between the first record of the phenomenon, by Anaxagoras, and Mr. Howard's observations in 1802, during which time the fact was disputed most strenuously by many, while, in our time, Professor Dewar's explanations of the same, upon intelligible and satisfactory principles, have confirmed the statements made centuries ago. How few the years, in comparison, since Keely's grand discovery first broke upon his own mind, which he has devoted to experiment,