1900.] on Eigh-Speed Navigation Steam Turbines. 237 



order that the speed of revolution may be reduced for the application 

 of the power. The improvements that have been made in Bianca's 

 steam turbine by De Laval are firstly, the ordinary steam jet is re- 

 placed by a diverging conical jet, which permits of the expansion of 

 the steam before it emerges from the jet, and so transforming the 

 potential energv of the high-pressure steam into kinetic energy of 

 velocity in the direction of flow. 



Secondly, the crude paddle-wheel of Bianca is replaced by a 

 wheel of the strongest steel, fringed round the periphery with little 

 cupped blades of steel, somewhat analogous to the buckets of a Pelton 

 water-wheel. 



Lastly, the steel wheel is mounted on a long and somewhat elastic 

 shaft, to allow of its easy and free motion, and on one extremity of 

 this shaft is mounted the pinion of the spiral reduction gear. 



The speeds of revolution of the steam-wheels of De Laval's 

 turbine are from 10,000 to 30,000 revolutions per minute, according 

 to the size, involving peripheral speeds up to 1200 feet per second, 

 or about one-half the speed of the projectile from a modern cannon. 

 Such speeds are necessary to obtain power economically from the 

 high-pressure steam jet, issuing from 3000 to 5000 feet per second 

 as calculated by Bankine. 



It is somewbat remarkable that not till a century after Bianca, 

 the piston or ordinary reciprocating engine made its first appearance, 

 in about the year 1705, and has since become one of the chief factors 

 in the great mechanical and engineering growths of the last century. 

 During this period the steam turbine seems to have been, practically 

 speaking, neglected, which is somewhat remarkable in view of the 

 numerous attempts of inventors to construct a rotary engine, attempts 

 which had no practical results. 



In the year 1884, the advent of the dynamo-electric machine, and 

 the development of mechanical and electrical engineering, created an 

 increased demand for a good high-speed engine. Engineers were 

 becoming more accustomed to high speeds of revolution, for the 

 speed of dynamos was at this time from 1000 to 2000 revolutions 

 per minute, of centrifugal pumps from 300 to 1500, and wood-working 

 machinery from 3000 to 5000 ; and Sir Charles Wheatstone had 

 made a tiny mirror revolve at a speed of 50,000 revolutions per 

 minute for apparatus for measuring the velocity of light. The 

 problem then presented itself of constructing a steam turbine, or 

 ideal rotary engine, capable of working with good economy of steam 

 at a moderate speed of revolution, and suitable for driving dynamos 

 without the intervention of reduction gearing. To facilitate the 

 problem, the dynamo was also considered with the view of raising 

 its speed of revolution to the level of the lowest permissible speed, 

 of the turbine engine. In other words, to secure a successful com- 

 bination, the turbine had to be run as slowly as possible, and the 

 dynamo speed had to be raised as much as possible, and up to the 

 same speed as the turbine, to permit direct coupling. 



