gradual diminution of transparency in natu ral substances, we shall see reason, (as sir John Herschel observes,) to admit that the latter quality, instead of being the opposite of the former, is only its extreme lowest degree.'* To render the affirmative, negative, and comparative facts more available, lord Bacon suggests that a tabular arrangement of them should be adopted. It is in this part of the Novum Organum that the author proceeds to exemplify his inductive method with reference to Heat. His collection of facts is allowed by Bacon's warmest admirers to be imperfect, yet, in the opinion of Professor Playfair, his ablest and most eloquent commentator,—it is extremely judicious, and the whole disquisition highly interesting. - Having, therefore, cautiously examined all the assembled data,-whether affirmative, negative, or comparative, we must then, *Herschel's Nat. Phil. § 135. after numerous' rejections and exclusions,' (as before observed,*) elicit some few principles, common to every case; and having verified these, by trying if they will account for the phenomena which they represent, we must, by the same process of rejections and exclusions,' endeavour to reduce the principles which we have already obtained to some or one (if possible) more general. When we can advance no higher, the ultimate axiom must be assumed as the cause, and then verified in the same manner as the subordinate principles. If it account for all the phenomena, then we have rightly interpreted nature; and the law which was the object of our search, is evolved. Some learned writers have supposed that Bacon's precepts relate only to physics; but the author himself designed them for all other sciences; nor does there appear any ground for asserting that the inductive me * Ante p. 146.-For 'conclusions' read exclusions. dew, which under certain circumstances exhibit colour; but they have nothing in common with flowers, metals, and wood, except the colour itself. Of the second kind of solitary instances examples may be found in the variegated veins which are to be seen in some of our beautiful marbles; for these, principally, at least, differ only in colour, and not so much in substance or structure. The various colours of flowers offer another instance. 2. Instantiæ Migrantes, or migrating instances, are those in which the nature or property under consideration, travels or passes from one state to another,-from less to greater, or from greater to less; approaching to perfection in the one case, and in the other, verging towards decay. In illustration of this class, Professor Playfair refers to the fossil shells which we see so perfect in figure and structure in limestone, and gradually losing themselves in the finer marbles, till they are no longer distinguish able.* A more striking illustration, perhaps, may be drawn from the phenomenon of what is commonly called the attraction of cohesion. In hard bodies, such as the diamond or steel, we find this force extremely powerful; in caoutchouc it is very weak; liquids exhibit it in a still less degree; and if we apply the irresistible power of the voltaic battery to water, for instance, we may altogether destroy the cohesion of its particles, and convert the whole into its constituent gases of hydrogen and oxygen. The atmospheric pressure affords another illustration: If we take a barometer in our Playfair's Prelim. Diss. p. 462. Even the colours of fossil shells belonging to species that are extinct, (as well as their figure and structure,) are sometimes preserved in so perfect a state that a common observer would suppose that they had just been taken from living testacea. Some fossil fish likewise retain their gaudy dress: one in the author's possession, found in the coal formation of Eisleben, is almost as bright in its hues as the brilliant gold-fish which enliven our ornamental tanks. there is an analogy or similitude in some particulars, though in others a great diversity.* The telescope and microscope compared with the eye may be mentioned as examples. Bacon's ear-spectacle, (or ear-trumpet, as it is now named,) and the concave roof of the dungeons of Syracuse, commonly called the 'ear of Dyonisius,' by which that tyrant used to listen to the words and whispers of his prisoners, are examples of a partial conformity with the construction of the human ear. • Strictly speaking, Analogy signifies a similitude of proportions; but in a looser and translated sense it has been used not merely with reference to the relation of one quantity to another, but as signifying all similitude of relations whatsoever. In common discourse, things are said to be analogous when they are, in fact, only similar. See Berkeley's Works, vol. 2, p. 63. In a short and luminous section, this great master of our language, and most acute logician, fully elucidates a subject which has produced not a little perplexity in the arguments of some of our theological writers. Bp. Berkeley's reasonings on this head have been ably illustrated by Bp. Copleston in his well-known Four Discourses,' pp. 122-141. |
