speak principally of the act of {76} _Invention_, which is requisite in every inductive inference. [Note 6\2: _Analyt. Prior._ lib. ii. c. xxiii. Περὶ τῆς ἐπαγωγῆς.] [Note 7\2: The syllogism here alluded to would be this:-- Mercury, Venus, Mars, describe ellipses about the Sun; All Planets do what Mercury, Venus, Mars, do; Therefore all Planets describe ellipses about the Sun.] [Note 8\2: Εἰ οὖν ἀντιστρέφει τὸ Γ τῷ Β καὶ μὴ ὑπερτείνει τὸ μέσον.--Aristot. _Ibid._] 4. Although in every inductive inference, an act of invention is requisite, the act soon slips out of notice. Although we bind together facts by superinducing upon them a new Conception, this Conception, once introduced and applied, is looked upon as inseparably connected with the facts, and necessarily implied in them. Having once had the phenomena bound together in their minds in virtue of the Conception, men can no longer easily restore them back to the detached and incoherent condition in which they were before they were thus combined. The pearls once strung, they seem to form a chain by their nature. Induction has given them a unity which it is so far from costing us an effort to preserve, that it requires an effort to imagine it dissolved. For instance, we usually represent to ourselves the Earth as _round_, the Earth and the Planets as _revolving_ about the Sun, and as _drawn_ to the Sun by a Central Force; we can hardly understand how it could cost the Greeks, and Copernicus, and Newton, so much pains and trouble to arrive at a view which to us is so familiar. These are no longer to us Conceptions caught hold of and kept hold of by a severe struggle; they are the simplest modes of conceiving the facts: they are really Facts. We are willing to _own_ our obligation to those discoverers, but we hardly _feel_ it: for in what other manner (we ask in our thoughts) could we represent the facts to ourselves?