1903.] EMMET—THE CURTIS STEAM TURBINE. 69 
the results of these experiments gave us data which showed great 
commercial possibilities, and since that time work has gone on on 
a large scale in the production of commercial machines. The con- 
tracts for these machines now aggregate 230,000 H. P. in turbine- 
driven electric generating units, the largest size so far built being 
7500 H. P. Thus a great industry has been brought into existence 
in a very short time, and since the work has all been done in one 
place and by a few persons very little information concerning it has 
reached the public. This paper is the first printed matter which 
has appeared on the subject. 
The reason for this immense demand and production, without 
publicity and in so short a time, is that the improvements effected 
are radical in economy, simplicity and efficiency of action. 
All improvements in prime movers are of great importance to 
the engineering world. The steam turbine is destined to effect the 
first really great improvement since the days of Watt, and the forms 
of Curtis turbine here described make the first great stride in 
advance of other steam engines. 
Every efficient steam engine must provide means by which a fair 
proportion of the expansive force of steam can be converted into 
useful work. In the engines of James Watt and his successors this 
result is accomplished in various degrees by the application of pres- 
sure from the steam to moving pistons. In steam turbines the 
expansive force imparts motion to the steam itself, and this motion 
is given up to a revolving part by impacts of the moving steam 
upon it. 
The idea of the steam turbine is quite simple, and is similar to 
that of the water turbine or impulse wheel. The practical difficulty 
which has heretofore prevented the development of good steam 
turbines lies in the very high velocity which steam can impart to 
itself in expansion, and the difficulty in efficiently transferring this 
motion to wheels at speeds practicable for construction or practical 
use. Steam expanding from 150 pounds gauge pressure per square 
inch into the atmosphere is capable of imparting to itself a speed 
of 2950 feet per second, and if it is expanded from 150 pounds 
gauge pressure into a 28-inch vacuum it can attain a velocity of 
4010 feet per second. The spouting velocity of water discharged 
from a nozzle with too feet head is 80 feet per second. These 
figures illustrate the very radical difference of condition between 
water turbines and steam turbines. In both water and steam tur- 
