1900.] on High-Speed Navigation Steam Turbines. 239 



in the steam turbine, the next problem was the turbine itself. The 

 laws regulating the flow of steam being well known (which was not the 

 case in Hero's time), various forms of steam turbine were considered, 

 and it appeared desirable to adopt in principle some type that Lad 

 been both successful in the water turbiue, and also easily adapted to 

 a multiple or compound formation, a construction in which the steam 

 should pass successively through a series of turbines one after the 

 other. 



The three best known of water turbines are the outward flow, the 

 inward flow, and the parallel flow, and of these the latter appeared to 

 be the best adapted for the multiple or compound steam turbine, for 

 reasons which will afterwards appear. 



The object in view being to obtain a good coefficient of efficiency 

 from the steam with a moderate speed of revolution and diameter of 

 turbine wheel, it becomes essential that the steam shall be caused to 

 pass through a large number of successive turbines, with a small 

 difference of pressure urging it through each individual turbine of 

 the set, so that the velocity of flow of the steam may have the proper 

 relation to the peripheral velocity of the turbine blades to secure the 

 highest degree of efficiency from the steam, conditions analogous to 

 those necessary for high efficiency in water turbines. A large 

 diameter of turbine wheel, it is true, would secure a moderate speed 

 of revolution, but this may be dismissed at once for the simple 

 reason that the frictional resistance of such a disc revolving at the 

 immense peripheral velocity, in the exhaust steam, would make it a 

 most inefficient engine. 



In the year 1884, a compound steam turbine engine of 10 horse- 

 power and a modified high-speed dynamo were designed and built 

 for a working speed of 18,000 revolutions per minute. This machine 

 proved to be practically successful, and subsequently ran for some 

 years doing useful work, and is now in the South Kensington Museum. 



This turbine engine consisted of two groups of fifteen successive 

 turbine wheels, or rows of blades, on one drum or shaft within a 

 concentric case on the right and left of the steam inlet, the moving 

 blades or vanes being in circumferential rows projecting outwardly 

 from the shaft, and nearly touching the case, and the fixed or guide 

 blades being similarly formed and projecting inwardly from the case 

 and nearly touching the shaft. A series of turbine wheels on one 

 shaft were thus constituted, each one complete in itself, like a paral- 

 lel flow water turbine, but unlike a water turbine, the steam after 

 performing its work in each turbine passed on to the next, preserving 

 its longitudinal velocity without shock, gradually falling in pressure 

 on passing through each row of blades and gradually expanding. 

 Each successive row of blades was slightly larger in passage-way 

 than the preceding, to allow for the increasing bulk of the elastic 

 steam, and thus its velocity of flow was regulated so as to operate 

 with the greatest degree of efficiency on each turbine of the series 

 (Fig. 1). 



