At the end of his seven years' apprenticeship, Samuel spent another year in the other royal dockyards, and at the Naval College at Portsmouth. He then went to sea as Captain Macbridge's guest, whose ship was one of Lord Keppel's fleet, and on this occasion he suggested sundry improvements in the apparatus of a ship, which were executed in Portsmouth Dockyard. In consequence of the abilities manifested by Bentham, many advantageous appointments were offered him; these were, however, refused, and in 1780 he embarked for the Continent, in order to obtain greater experience in the different practices in the art of naval construction. After having visited Holland he proceeded to Russia, and was well received at St. Petersburgh by the English Ambassador, Sir James Harris, who introduced him to the best society, and through whose means he became acquainted, among others, with Prince Potemkin, and the celebrated traveller, Pallas. Whilst on a visit to the large manufactory of Count Demidoff, Bentham constructed a sort of amphibious vehicle, in the form of a boat, and capable of serving as an ordinary wheel-carriage, and also, when necessity required, of being navigated across, or along a stream of water. This invention he subsequently patented, and likewise extended its utility by constructing the carriages so as to serve as army baggage-waggons, a supply of which Prince Potemkin ordered to be furnished to a regiment at Jassy. They were also introduced into England about the year 1793, when the Duke of York requested that one should be built for the English service, which was successfully tried on the River Thames. In gratitude to Count Demidoff for the facilities which he had afforded him in constructing this carriage, Bentham invented for the use of the Count's factory, a wood-planing machine, which could also be used for making mouldings by changing the cutting tool. Bentham's stay in Russia was prolonged for a greater period than he originally intended, from his having become attached to a Russian lady of considerable rank and beauty; but although this attachment was mutual, nothing came of it, owing to the opposition of the lady's relatives, on the score of Bentham being a foreigner. During this period Bentham had the direction of the Fontanka Canal, in connection with which he invented a peculiar form of pile-driving machine, in which the weight was attached to a sort of endless ladder, moved by a man stepping on it, on the principle that a man's weight exceeds considerably his muscular strength.