Every one, again, believes in certain facts that are asserted by navigators, explorers, and geographers, respecting the existence, position, and products of various countries of the globe. Every one, further, believes in certain deductions derived from these facts by naturalists, geologists, astronomers, and so forth. The belief is owing to the unanimous testimony of all these confessedly competent authorities; but whenever they are seen to differ among themselves, the public withholds its entire belief, and either doubts or disbelieves the things asserted. Thus the public is at this day doubtful and divided whether there is such a creature as the sea-serpent. Similarly the public is dubious--for it must needs be so if any section of it is so--whether a certain explorer who was authoritatively sent out about a dozen years ago conjointly by the French Government and Institute, was, in any degree, justified in bringing home the account he did of there being a tribe of men in the interior of Africa having tails, whether this unexpected information is, in any important particular, true. The two last examples have been furnished by material science. I will now draw one from the other department, with the view of indicating that in non-material science also, numerous propositions circulate among the public that are franked by the same principle to pass as undoubted truth. Such is the maxim of heathen philosophy, recorded by Cicero in his "Officiis": "Do not to another what you would not he should do to you"; or the same maxim, in its modified form, as given in the New Testament, with the characteristic omission of the negative. The truth of this moral maxim is universally admitted, because it is supposed that no person of presumable moral judgment has ever been known to call it in question. It would seem, then, that this criterion of truth is--what confessedly, or from easy proof, it is predicable that no other criterion of truth is--a general criterion of truth. I will, however, restrict this pretension to the statement--to be hereafter more largely explained--that it is a general criterion of truth to the public as such, to the public considered as a public; for, indeed, it is not properly usable at all by anyone except in the character of a member of the public. This means that it is a general criterion of truth in the following way: it is applicable to the verification of all truth, so far as it admits of being verified before the public, and made the common property of the community.