In his last letter our San Francisco correspondent, in mentioning the death of the celebrated engineer, John Ericsson, a Scandinavian by birth, but an American by adoption, stated that the caloric engine—which made Ericsson's fame—was a failure in practice, and that he would be remembered as the author of the screw propeller. his is, of course, a great mistake; John Ericsson was by no means the author or inventor of the screw propeller, or of the caloric engine, or of monitors; in fact, he was far more an improver of other men's inventions, than an inventor himself.
Most of us owe our presence in China, and the greater part of our comforts now we are here to the invention of the screw propeller, and it is therefore worth while to look a little more closely into its history: and probably most of our readers will be surprised to hear that it is more than two hundred years old. The first form of it, suggested by Hooke in 1680, consisted of a spiral blade, making one convolution round its stem. Then two half-convolutions of a double-threaded screw were used, and the later changes have been in the direction of a reduction of the length of the spiral. It was not until the invention of the steam-engine that the screw-propeller could be made of practical use, and the first patent for an "aquatic propeller," consisting of a screw entirely immersed, and intended to be placed either at the head, stern or side of a vessel, was taken out in England by Lyttelton in 1794. The first application of the screw propeller for propulsion of a sea-going vessel was ten years later, and the author of it was Colonel John Stevens of Hoboken, New Jersey, US.A. He constructed a boat, fifty! feet long, with two screws, which attained considerable speed; so that the invention of twin screws is, after all, only a revival. The machinery of this boat is still to be seen in the Stevens Institute of Technology at Hoboken and in 1844 this machinery was placed in a boat specially built on the lines of Stevens' original hull, which it pro-elled at the rate of eight miles an hour. The modern twin screws are driven by independent sets of engines, and this is claimed as one of their great advantages; Col. Stevens' were actuated by a single cylinder placed between the two screw shafts which were driven by connecting-rods from the two ends of the cross-head. In 1806 Col. Stevens built a second and a larger boat with a single screw; but at this period the steam-engine itself was only in its infancy, and arear improvements had to be made in it before steam propulsion by the screw propeller could be brought into practical use. The steam engines of that date worked so slowly that gearing had to be used to get sufficient speed in the screw shaft; this gearing was still in use in the time of men now in China; but its liability to break down by the stripping of the wheels was the great drawback to the employment of the screw.
The man whose inventive genius brought the screw propeller into prac tical use in England—and England has: been the chosen home of the screws steamer as America of the paddle-boat, was Francis Pettit Smith, a farmer of Romney, who was afterwards knighted in recognition of the value of his me vention. In 1834 he made a model boat, lof May, 1836. ile built a ten-ton and took out his patent on the 31st
boat, fitted with a six horse-power engine, which was tried successfully on the Thames and the coast, but' the steamer which first demonstrated in England the value of the screw on something more than an experimental ale, was the Archimedes, built by the Messrs. Rennie for Mr. Smith in 1888, She was 155 feet long, 237 tons burden, and 90 horse-power. In appearance she very much resembled the gunboats that came out to China after the Crimean war and did duty here faithfully for so many years, In 1842 the British Admiralty determined to make a conclusive trial of the invention, and they built two gunboats on the same lines, the Ztattlér with a screw propeller, and the Alecto with paddle wheels. The two vessels when ready were subs mitted to an exhaustive series of com petitive trials, and the screw boat was the ultimate conqueror.
Meanwhile John Ericsson had been proceeding on the same lines as Mr. Smith, and he took out his English patent on the 13th of July, 1836, six Weeks after his rival. In April, 1887, is first vessel, the Francis B. Ogden; was tried, and was successful in towing an American ship of 700 tons, the Toronto, to sea at the rate of 4} miles an hour ayainst wind and tide. In Birkenhead built for him a larger the following year Messrs. Laird of
vessel, the Jtobert F. Stockton, which
Text read from the printed page and cleaned; old type leaves the occasional error.