The little _Enterprise_ was engined by Wilson of London, in 1872, with a pressure of 150 lb.; the _Sexta_, engined by the Ouseburn Engine Works of Newcastle-on-Tyne in 1874, had boilers with a pressure of 120 lb. and triple-expansion engines working on three cranks; the _Propontis_, engined in the same year by Elder, of Glasgow, was also fitted with triple-expansion engines. Mr. Perkins’ tri-compounds came out in the ’seventies, the _Isa_ (yacht) in 1879, with a pressure of 120 lb.; and there were a few others. With the exception of the _Isa_, all the others may well be designated experiments that failed, and it was owing to the success of this little yacht that the possibility of the ordinary boiler for still higher pressures suggested itself.[94] [94] Paper on “Cargo Boat Machinery,” by Mr. J. F. Walliker, Institute of Marine Engineers. The _Propontis_, built in 1864, was re-engined and fitted with tri-compounds and new boilers in 1874. The boilers (of the water-tube type) were a failure, and were replaced by cylindrical boilers in 1876, at a reduced pressure of 90 lb. With these she worked till 1884, when her boilers were renewed. Dr. Kirk declared “that the want of a proper boiler had delayed the introduction of the triple expansion.” Plates of five tons in weight and upwards are in common use for boiler shells, yet in 1881 hardly a firm on the north-east coast would undertake to build a boiler for 150 lb. pressure. The success of the triple engine resulted in many vessels being converted and fitted with new boilers, while others were re-engined. Messrs. Palmer, in the _James Joicey_, fitted an interchangeable crank-shaft with the crank-pin on the centre engine, made with a coupling at each end to fit into a recess in the web. It was seen at quite an early stage of tri-compounds that the three-crank engine, with cranks at equal angles, from its easy turning moments, would be the most satisfactory, and its universal adoption in new engines was only the work of a very short time. The steamers _Aberdeen_ and _Claremont_, both launched in 1881, were the first to have commercially successful triple-expansion engines. As to how high steam-pressures may go, it is recorded that the yacht _Salamander_, with triple-expansion engines, had the valve set at 600 lb. The invention of the turbine has been the most remarkable event in the modern history of the steam-engine. The following passages, taken from the Hon. C. A. Parsons’ paper on turbines, read at the Engineering Exhibition, 1906, give an account of its adoption for purposes of steam navigation: