But is it in fact found that undisputed points are always such as have been the most carefully examined as to the evidence on which they rest? that facts or principles which are taken for granted, without controversy, as the common basis of opposite opinions, are always themselves established on sufficient grounds?  On the contrary, is not any such fundamental point, from the very circumstance of its being taken for granted at once, and the attention drawn off to some other question, likely to be admitted on insufficient evidence, and the flaws in that evidence overlooked?

Experience will teach us that such instances often occur:  witness the well-known anecdote of the Royal Society; to whom King Charles II. proposed as a question, whence it is that a vessel of water receives no addition of weight from a live fish being put into it, though it does, if the fish be dead.  Various solutions, of great ingenuity, were proposed, discussed, objected to, and defended; nor was it till they had been long bewildered in the inquiry, that it occurred to them to try the experiment; by which they at once ascertained that the phenomenon which they were striving to account for,—­which was the acknowledged basis and substratum, as it were, of their debates,—­had no existence but in the invention of the witty monarch.[3]

Another instance of the same kind is so very remarkable that I cannot forbear mentioning it.  It was objected to the system of Copernicus when first brought forward, that if the earth turned on its axis, as he represented, a stone dropped from the summit of a tower would not fall at the foot of it, but at a great distance to the west; in the same manner as a stone dropped from the mast-head of a ship in full sail, does not fall at the foot of the mast, but towards the stern.  To this it was answered, that a stone being a part of the earth obeys the same laws, and moves with it; whereas, it is no part of the ship; of which, consequently, its motion is independent.  This solution was admitted by some, but opposed by others; and the controversy went on with spirit; nor was it till one hundred years after the death of Copernicus, that the experiment being tried, it was ascertained that the stone thus dropped from the head of the mast does fall at the foot of it![4]

Let it be observed that I am not now impugning any one particular narrative; but merely showing generally, that what is unquestioned is not necessarily unquestionable; since men will often, at the very moment when they are accurately sifting the evidence of some disputed point, admit hastily, and on the most insufficient grounds, what they have been accustomed to see taken for granted.

The celebrated Hume[5] has pointed out, also, the readiness with which men believe, on very slight evidence, any story that pleases their imagination by its admirable and marvellous character.  Such hasty credulity, however, as he well remarks, is utterly unworthy of a philosophical mind; which should rather suspend its judgment the more, in proportion to the strangeness of the account, and yield to none but the most decisive and unimpeachable proofs.