We think this remark perfectly just; and we would point out besides, in appreciating Sir W. Hamilton's merits, that his appetite for facts was useful to philosophy, as well as his appetite for speculation. But the person whose usefulness to philosophy we prefer to bring into the foreground, is Platner himself. He spent three weeks in patient examination of this blind man, and the tenor of his report proves that his sagacity in interpreting facts was equal to his patience in collecting them. The rarity of all such careful and premeditated observation of the facts of mind, appears to us one main reason why (what Mr Mill calls) the _psychological_ theory finds so little acceptance; and why those who maintain that what now seems a mental integer was once a multiplicity of separate mental fragments, can describe the antecedent steps of the change only as a _latens processus_, which the reader never fully understands, and often will not admit. Every man's mind is gradually built up from infancy to maturity; the process is always going on before our eyes, yet the stages of it--especially the earliest stages, the most pregnant with instruction--are never studied and put on record by observers trained in inductive logic, knowing beforehand what they ought to look for as the _sine quâ non_ for proving or disproving any proposed theory. Such cases as that cited by Platner--cases of one marked congenital defect of sense, enabling us to apply the Method of Difference--are always within reach; but few Platners are found to scrutinize and record them. Historians of science describe to us the laborious and multiplied observations, and the elaborate precaution for ensuring accuracy of observation, which recent chemical and physical inquirers have found indispensable for the establishment of their results. We cannot, therefore, be surprised that mental philosophers, dealing with facts even more obscure, and careless about enlarging, varying, authenticating their records of particular facts, should have had little success in establishing any results at all.