Roger Bacon, to whom the invention or knowledge of gunpowder has been attributed by some, would stand a very poor chance among the men of science of the present day: it is not now the man who conjectures a possibility, but he who demonstrates a fact, that is hailed as the discoverer. The following series of possibilities are curiously interesting, both from their partial subsequent realization, and from the simple credulity with which Bacon gives us that which he had known "a wise man explicitly excogitate." "Instruments of navigation can be made, men being the propelling agents, that the largest river and sea barks can be borne along (one man only managing them) with greater speed than if they were full of navigators. Carriages can also be constructed which may be moved without animals, with an inestimable impetus; so that one would think that they were the armed chariots with which they fought in ancient times. Instruments for flying can also be made, so that a man sitting in the centre of the machine, and turning an engine, by which artificial wings may strike the air in the manner of a bird flying. An instrument also can be made, small in magnitude, for elevating and lowering almost infinite weights, than which nothing is more useful in mischances, for by an instrument of the length of three fingers, and of the same breadth or less, a man may extract himself and companions from all danger of prison, and elevate and lower them. An instrument can also be made by which one man may draw to himself a thousand men, by force and against their will. Instruments for walking on the sea can also be made, and in rivers to the bottom without corporal peril. For Alexander the Great used them that he might see the secrets of the sea, according to the relation of Ethicus the astronomer. "These things, indeed, are of antiquity and of our times, and are certain, except the instrument for flying, which I have not seen, nor have I known a man who has, but I know a wise man who has explicitly excogitated it; and an infinity of other things can be made, as bridges over rivers, can be made without columns or any support, and machines or unheard of engines." The ultra admirer of the ancients will see in this, if not an accurate relation of facts, which with the exception of the flying it purports to be, at least a wonderful perception of practicabilities; and railroads, diving-bells, suspension-bridges, &c., will be so many circumstantial corroborations of the correctness of his view. We, however, are rather disposed to regard them as ingenious extravagances. Predictions of the success of science are always on the safe side. If in the present day one were to say, that we shall be able to see the inhabitants of Jupiter, or even converse with them, it would be a prophecy which could never be negatived, which might be the case if we said such things were impossible.