102 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
siderable backward velocity, and to obtain the highest efficiency it 
is necessary to reduce this backward velocity by increasing the ve- 
locity of the wheel to the uttermost. The strongest materials, how- 
ever, do not permit of a close approach to the speed necessary for 
the maximum efficiency; yet in this turbine, owing to the compara- 
tive absence of losses, which are present to some extent in the other 
types (and which we will consider presently), the efficiency of this 
turbine compares favorably 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 purpose 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 It was superseded in 1892 by the damping 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-fitting 
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 400 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 
