and the female the body; that the body being liable to decay, and of a transitory nature, it is necessary for its well-being that its disintegration and nutrition should balance one another; that sensation may be compared to the impression of a seal on wax, the wax receiving form only, but no substance or matter; that imagination arises from impressions thus made, which endure for a length of time, and that this is the origin of memory; that man alone possesses recollection, but animals share with him memory--memory being unintentional or spontaneous, but recollection implying voluntary exertion or a search; that recollection is necessary for acting with design. It is doubtful whether Aristotle believed in the immortality of the soul, no decisive passage to that effect occurring in such of his works as are extant. [Sidenote: Causes of Aristotle's success and failure.] Aristotle, with a correct and scientific method, tried to build up a vast system when he was not in possession of the necessary data. Though a very learned man, he had not sufficient knowledge; indeed, there was not sufficient knowledge at that time in the world. For many of the assertions I have quoted in the preceding paragraph there was no kind of proof; many of them also, such as the settling of the heavy and the rise of the light, imply very poor cosmic ideas. It is not until he deals with those branches, such as comparative anatomy and natural history, of which he had a personal and practical knowledge, that he begins to write well. Of his physiological conclusions, some are singularly felicitous; his views of the connected chain of organic forms, from the lowest to the highest, are very grand. His metaphysical and physical speculations--for in reality they are nothing but speculations--are of no kind of value. His successful achievements, and also his failures, conspicuously prove the excellence of his system. He expounded the true principles of science, but failed to apply them merely for want of materials. His ambition could not brook restraint. He would rather attempt to construct the universe without the necessary means than not construct it at all. Aristotle failed when he abandoned his own principles, and the magnitude of his failure proves how just his principles were; he succeeded when he adhered to them. If anything were wanting to vindicate their correctness and illustrate them, it is supplied by the glorious achievements of the Alexandrian school, which acted in physical science as Aristotle had acted in natural history, laying a basis solidly in observation and experiment, and accomplishing a like durable and brilliant result. [Sidenote: Biography of Zeno.]