In another part of his specification Trevithick described the screw-propeller as "a screw or a number of leaves placed obliquely round an axis similar to the vanes of a smoke-jack, which shall be made to revolve with great speed in a line with the required motion of the ship, or parallel to the same line of motion." In a second part of the specification, he described a plunger or pole-engine in which the steam worked at high-pressure. The first engine of this kind was erected by Trevithick at Herland in 1815, but the result was not equal to his expectations, though the principle was afterward successfully applied by Mr. William Sims, who purchased the patent-right. In this specification Trevithick also described a tubular boiler of a new construction for the purpose of more rapidly producing high-pressure steam, the heating surface being extended by constructing the boiler of a number of small perpendicular tubes, closed at the bottom, but all opening at the top into a common reservoir, from whence they received their water, and into which the steam of all the tubes was united. While Trevithick was engaged in these ingenious projects, an event occurred which, though it promised to issue in the most splendid results, proved the greatest misfortune of his life. We refer to his adventures in connection with the gold mines of Peru. Many of the richest of them had been drowned out, the pumping machinery of the country being incapable of clearing them of water. The districts in which they were situated were almost inaccessible to ordinary traffic, all transport being conducted on the backs of men or of mules. The parts of an ordinary condensing engine were too ponderous to be carried up these mountain heights, and it was evident that, unless some lighter sort of engine could be employed, the mines in question must be abandoned. Mr. Uvillé, a Swiss gentleman interested in South American mining, came over from Peru to England in 1811 for the purpose of making inquiries about such an engine, but he received no encouragement. He was about to return to Lima, in despair of accomplishing his object, when, one day, accidentally passing a shop-window in Fitzroy Square, he caught sight of an engine exposed for sale which immediately attracted his attention. It was the engine constructed by Trevithick for his first locomotive, which he had sold some years before, on the sudden abandonment of the exhibition of its performances in London. Mr. Uvillé was so much pleased with its construction and mode of action that he at once purchased it and took it out with him to South America. Arrived there, he had the engine transported across the mountains to the rich mining district of Pasco, about a hundred miles north of Lima, to try its effects on the highest mountain ridges.