as the comic poet has it; but what you want to learn is the [Sidenote: E] nature of air, and the property in virtue of which its repeated contact has coloured the bronze.’ Diogenianus said that it was. ‘And I too,’ Theon continued, ‘my young friend, let us follow the quest together; and first, if you will agree, ask why olive oil produces a more copious rust on the metal than other liquids; it does not, of course, actually make the deposit, being pure and uncontaminated when it is applied.’ ‘Certainly not;’ said the young man, ‘the real cause appears to me to be something different; the oil is fine, pure, and transparent, so the rust when it meets it is specially evident, whereas with other liquids it becomes invisible.’ ‘Excellent,’ said Theon, ‘my [Sidenote: F] young friend, that is prettily put. But consider also, if you please, the cause given by Aristotle.’ ‘I do please’, he said. ‘Aristotle says that the rust, when it comes over other liquids, passes invisibly through and is dispersed, because the particles are irregular and fine, whereas in the density of oil it is held up and permanently condensed. If, then, we can frame some such hypothesis for ourselves, we shall not be wholly at a loss for a spell to charm away this difficulty.’ IV. We encouraged him and agreed, so he (Theon) went [Sidenote: 396] on to say that the air of Delphi is thick and close of texture, with a tenseness caused by reflection from the hills and their resistance, but is also fine and biting, as seems to be proved by the facts of digestion of food. The tenuity allows it to enter the bronze, and to scrape up from it much solid rust, which rust again is held up and compressed, because the density of the air does not allow it a passage through; but the deposit breaks out, because it is so copious, and takes on a rich bright colour on the surface. We applauded this, but the stranger remarked that either hypothesis alone was sufficient for the argument. ‘The fineness’, [Sidenote: B] he went on, ‘will be found to be in contradiction to the density of which you speak, but there is no necessity to assume it. The bronze, as it ages, exhales or throws off the rust by its own inherent action; the density holds together and solidifies the rust, and makes it apparent because of its quantity.’ Theon broke in: ‘What is to prevent, Sir, the same thing being both fine and dense, as silks or fine linen stuffs, of which Homer says _And from the close-spun weft the trickling oil will fall_,[85] where he indicates the minute and delicate workmanship of the fabric by the fact that the oil would not remain, but trickled [Sidenote: C] or glided off, the fineness at once and the density refusing it a passage. And, again, the scraping up of the rust is not the only purpose served by the tenuity of the air; it also makes the colour itself pleasanter to the eye and brighter, it mingles light and lustre with the blue.’