We must draw a wide distinction between the things which Bacon relates as upon credible authority, and the opinions which he professes himself to entertain from his own investigations. In almost every page we meet with something now considered extremely absurd, and with reason. But before the day of _printing_ there was very little _publishing_: a book which was written in one country, found its way but slowly into others, one copy at a time; and a man of learning seldom met those with whom he could discuss the probability of any narrative. The adoption of the principle that a story must be rejected because it is strange, would then have amounted to a disbelief of all that had been written on physics; a state of mind to which we cannot conceive any one of that age bringing himself. Nor can we rightly decide what opinion to form of Bacon as a philosopher, until we know how much he rejected, as well as how much he believed. These remarks apply particularly to his alchemy: he does not say he had made gold himself, but that others had asserted themselves to have made it; and his account of the drink by which men had lived hundreds of years is a relation taken from another. Voltaire, in his Philosophical Dictionary, has overlooked this distinction, and has much to say in consequence. It was, however, no very strange matter that Bacon, who (if the 'Speculum Alchemiae' be really his, of which, from the style, we doubt) believed with many others that sulphur and mercury were the first principles of all bodies, should endeavour to compound gold, or should give credit to the assertions of those who professed to have done so. But there is not in Bacon's alchemy any direction for the use of prayers, fasting, or planetary hours. The great points by which Bacon is known are his reputed knowledge of gunpowder and of the telescope. With regard to the former, it is not at all clear that what we call gunpowder is intended, though some detonating mixture, of which saltpetre is an ingredient, is spoken of as commonly known. The passage is as follows:-- "Some things disturb the ear so much, that if they were made to happen suddenly by night, and with sufficient skill, no city or army could bear them. No noise of thunder could compare with them. Some things strike terror on the sight, so that the flashes of the clouds are beyond comparison less disturbing; works similar to which Gideon is thought to have performed in the camp of the Midianites. And an instance we take from a childish amusement, which exists in many parts of the world, to wit, that with an instrument as large as the human thumb, by the violence of the salt called saltpetre, so horrible a noise is made by the rupture of so slight a thing as a bit of parchment, that it is thought to exceed loud thunder, and the flash is stronger than the brightest lightning."--_Opus Majus_, p. 474.