for those who have read and understood that work, is chiefly for the sake of those who may not have had an opportunity of perusing the volume itself. One source of the general fallacy unquestionably is that influence of _abstraction_, to which I before alluded, as aided, and in a great measure perpetuated, by the use of language, and the common unavoidable modes of grammatical construction. We speak of the powers of a substance, of substances that have certain power--of the figure of a body, or of bodies that have a certain figure, in the same manner as we speak of the students of a university, or of a house that has a great number of lodgers; and we thus learn to consider the power, which a substance possesses, as something different from the substance itself, inherent in it indeed, but inherent, as something that may yet subsist separately. In the ancient philosophy, this error extended to the notions both of form and power. In the case of _form_, however, we have seen, that the illusion, though it lasted for many ages, did at length cease, and that no one now regards the _figure_ of a body, as any thing but the body itself. It is probable that the illusion, with respect to power, as something different from the substance that is said to possess it, would, in like manner, have ceased, and given place to juster views, if it had not been for the cause, which I am next to consider. This cause is the _imperfection of our senses_, the same cause which, in the other department of physics before examined by us,--the department, that relates to matter considered merely as existing in space,--we find to give occasion to all our inquiries into the compositions of bodies. In this department of physics, however, which relates to the successions of phenomena in time, the imperfection of our senses operates in a different way. It is not that which gives occasion to the necessity of inquiry; for we have seen, that senses, of the utmost accuracy and delicacy, could not, of themselves, and without experience, have enabled us to predict any one event, in the innumerable series of phenomena that are constantly taking place around us. But, though senses of the nicest discrimination could not have rendered inquiry into the successions of events superfluous, they would have saved us from much idle inquiry, and have given far greater precision, if not to our _rules_, at least to our uniform _practice_, of philosophizing.