326 The Hon. Charles A. Parsons [May 4, 



presently), the efficiency of this turbine compares favourably for 

 moderate and small powers. 



In this beautiful construction, developed with mechanical skill 

 and guided by an intimate acquaintance with the properties of steam 

 and materials, there are many minor features of interest. Among 

 them may be mentioned the elastic shaft, to permit of the rotation of 

 the turbine wheel about its dynamic axis. A device, consisting of 

 frictional damping washers, which had the same puipose as this 

 elastic shaft, was used in 1885 in the early development of the com- 

 pound steam turbine. It was superseded in 1892 by the damping 

 effect of thin films of oil between several concentric loosely-litting 

 tubes surrounding the bearings. 



The De Laval turbine has for many years been extensively used 

 on the Continent and in this country, in sizes up to about 40u horse- 

 power. Its chief use has been for the driving of dynamos, pumps, 

 fans, and motive power generally : and, owing to its very high angular 

 speed, it is necessary in most cases to use gearing, except when driving 

 very fast-running centrifugal pumps and fans. 



The gearing is of steel, and it is accurately cut with very fine 

 spiral teeth, and it works satisfactorily even at the speed of 30,000 

 revolutions per minute. 



Let us now consider the Curtis turbine. It ranks in a class by 

 itself, because it comprises the principle of the sinuous treatment of 

 expanded steam first put into extended commercial use by Mr. Curtis 

 under the auspices of the General Electric Company of America. 



This sinuous treatment of the steam consists in giving to it a high 

 initial velocity by passing it through a jet of the De Laval type, or a 

 group of such jets ; it then impinges on a ring of bucket-blades like 

 those used by De Laval, and after leaving the first row of such blades 

 it is caught by a ring or a sector of stationary bucket-blades set in 

 the reverse direction, and by them its direction is changed into that 

 of the next succeeding row of moving blades (there may be three 

 rows of moving blades in all and two sectors of fixed blades) : and the 

 height of each succeeding row is increased, to allow a greater area for 

 the steam as it flags in velocity after each rebound between the moving 

 and fixed blades. 



The object of this treatment is to transfer a large percentage of 

 the kinetic energy of the rapidly moving steam to the moving blades 

 and wheel, without the necessity of very high peripheral speeds of 

 blades, such as are necessary with the single-wheel type. As regards, 

 however, "multiple series action," the principle resembles the com- 

 pound turbine. 



The expansion process in nozzles, and subsequent sinuous treat- 

 ment of the steam, is repeated several times by four or more similar 

 wheels on the same axis, but in separate steam-tight chambers, until 

 the steam is fully expanded. 



If there are four such operations, the velocity of outflow from the 



