10. EMMET—THE CURTIS STEAM TURBINE. [April 2, 
bines the theoretical condition of maximum economy exists when 
the jet of fluid moves with a velocity equal to about twice that of 
the vane against which it acts. In water-wheels this relation is 
easily established under all conditions, while with steam the total 
power produces a velocity so high that the materials available for 
simple wheels and vanes are not capable of sustaining a proper 
speed relation to it under practicable conditions. 
Before the appearance of the Curtis turbine two practical methods 
of accomplishing fair economy had been devised, namely, the 
turbines of Carl De Laval, of Sweden, and of Hon. Charles Alger- 
non Parsons, of England, both of which were brought out more 
than fifteen years ago. 
In the De Laval turbine the total power of the steam is devoted 
to the production of velocity in an expanding nozzle, which pro- 
duces velocity very efficiently. The jet so produced is delivered 
against a set of vanes on a single wheel which, by an ingenious 
construction and method of suspension, is adapted to operation at a 
very high peripheral velocity. The very high rotative speed which 
this construction entails is made available for dynamo driving by 
very perfectly made spiral-cut gears which effect a ten-to-one speed 
reduction. The peripheral velocity of the wheel in the largest 
De Laval turbines is about 1200 feet per second, while the velocity 
which energy can impart to steam is over 4000 feet per second. 
Thus the wheel falls far short of the theoretically economical speed. 
In the Parsons turbine the steam is carried in an axial direction 
through the space provided, between a succession of internal revolv- 
ing cylinders and external stationary cylinders which enclose them. 
Both the internal and the external cylindrical surfaces are covered 
by many successive circles of vanes so arranged that the steam has 
to pass alternately through rows of moving and stationary vanes. 
In passing through this turbine the steam never acquires a speed 
which approaches the velocity which it attains in the De Laval 
nozzle ; but instead moves along alternately, acquiring velocity by 
expansion, and partially giving it up by impact with the moving 
vanes. 
Both of these turbines have attained some success, but neither, 
as thus far developed, affords sufficient advantage over the steam 
engine to cause any very rapid or radical change in engineering 
conditions, 
The important disadvantages of the De Laval type are, that it is 
| 
| 
