However the experienced philosopher may be convinced that _in themselves_ theories are nothing--that they are but collations of phenomena under a generic formula, which is useful only inasmuch as it groups these phenomena; yet it is difficult to see how, without these imperfect generalizations, any mind can retain the endless variety of facts and relations which every branch of science presents; still less, how these can be taught, learned, reasoned upon, or used. How could the facts of geology be recollected, or how, indeed, could they constitute a science without reference to some real or supposed bond of union, some aqueous or igneous theory? How could two chemists converse on chemistry without the use of the term affinity, and the theoretical conception it involves? How could a name be applied, or a nomenclature adopted, without that imperfect, or more or less perfect grouping of facts, which involves theory? As far as we can recollect, all the alterations of nomenclature which have been introduced, or attempted, proceed upon some alteration of theory. If not theory but hypothesis be objected to--not the imperfect generalization of phenomena, but a gratuitous assumption for the sake of collating them, this, although ground which should be trodden more cautiously, appears in certain cases unavoidable; in fact, is scarcely separable from theory. Had men not "lectured learnedly" about the two _fluids_ of electricity, we should not now possess many of the discoveries with which this science is enriched, although we do not, and probably never shall, know what electricity is. On the other hand, among professed physical philosophers, the great abuse of theories and hypotheses is, that their promulgators soon regard them, not as aids to science, to be changed if occasion should require, but as absolute natural truths; they look to that as an end, which is in fact but a means; their theories become part of their mental constitution, idiosyncrasies; and they themselves become partizans of a faction, and cease to be inductive philosophers. Another injury to science, in a great measure peculiar to the present day, arises from the number of speculations which are ushered into the world to account for the same phenomena; every one, like Sir Andrew Aguecheek, when he wished to cudgel a Puritan, has for his opinion "no exquisite reasons, but reasons good enough." In the periods of science immediately subsequent to the time of Bacon, men commenced their career by successful experiment; and having convinced the world of their aptitude for perceiving the relations of natural phenomena, enounced theories which they believed the most efficient to give a comprehensive generality to the whole. Men now, however, commence with theories, though, alas! the converse does not hold good--they do not always end with experiment.