While Trevithick lived at Rotherhithe, he entered upon a remarkable enterprise--no less than the construction of a tunnel under the Thames--a work which was carried out with so much difficulty by Sir Isambard Brunel some twenty years later. Several schemes had been proposed at different times for connecting the two banks of the river by an underground communication. As early as 1798, Ralph Dodd suggested a tunnel under the Thames between Gravesend and Tilbury, and in 1802 Mr. Vazie projected a tunnel from Rotherhithe to Limehouse. A company was formed to carry out the latter scheme, and a shaft was sunk, at considerable expense, to a depth of 76 feet below high water. The works were from time to time suspended, and it was not until the year 1807, when Trevithick was appointed engineer of the work, that arrangements were made for proceeding with the driftway under the bed of the Thames. After about five months' working, the drift was driven for a length of 953 feet, when the roof gave way and the water burst in. The opening was, however, plugged by clay in bags thrown into the river, and the work proceeded until 1028 feet had been accomplished. Then the water burst in again, and the process of plugging and pumping the water out of the drift was repeated. After seventy more feet had been added to the excavation, there was another irruption, which completely flooded the driftway, and the water rose nearly to the top of the shaft. This difficulty was, however, again overcome, and with great danger twenty more feet were accomplished; but the bursts of water became so frequent and unmanageable that at length the face of the drift was timbered up and the work abandoned. Trevithick, who had been promised a reward of £1000 if the tunnel succeeded, thus lost both his labor and his reward. The only remuneration he received from the Company was a hundred guineas, which were paid to him according to agreement, provided he carried the excavation to the extent of 1000 yards, which he did. Trevithick returned to Camborne in 1809, where we find him busily occupied with new projects, and introducing his new engine worked by water-power, the first of which was put up at the Druid mine, as well as in perfecting his high-pressure engine and its working by expansion. One of the first of such engines was erected at the Huel Prosper mine, of which he was engineer; and this, as well as others subsequently constructed on the same principle, proved quite successful. In 1815 Trevithick took out a farther patent, embodying several important applications of steam-power. One of these consisted in "causing steam of a high pressure to spout out against the atmosphere, and by its recoiling force to produce motion in a direction contrary to the issuing steam, similar to the motion produced in a rocket, or to the recoil of a gun." This was, however, but a revival of the ancient OEolipile described by Hero, and known as "Hero's engine."