100 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
more and more considerable extent, and this tendency is not confined 
alone to England, but is shown also on the Continent, and in the 
United States and Japan. It will give a clearer idea of the subject 
if we first of all examine more closely the characteristics of the steam 
turbine, and generally how it works. 
All turbines derive their power from the impact of the steam, or, 
more correctly speaking, from the momentum of the steam, flowing 
through them, just as a windmill receives its power from the wind. 
There are three principal types of turbines now in general use, as 
well as some which may be described as admixtures of these three 
classes. They differ essentially in some respects, more particularly in 
their methods of extracting the power from the steam. 
The first to receive commercial application, 1884, was the com- 
pound or multiple expansion steam turbine; the second was the De 
Laval or single-bucket wheel, in 1888, driven by the expanding steam 
jet; and, lastly, the Curtis turbine, in 1896, which comprises some of 
the principal features of the others combined with a sinuous treat- 
ment of the steam. 
In the compound turbine, the steam is caused to flow through a 
series of many turbine elements of gradually increasing size, grad- 
uated so as to allow of the expansion of steam in small increments of 
volume at each element, these increments of volume corresponding to 
the fall of pressure necessary to cause the steam to flow through each 
element. Each element consists of a row of guide blades and a row of 
moving blades. The guide blades are attached in circumferential 
rows to the case and project inwardly, and the moving blades are 
attached in: rows to a drum and project outwardly. The end of 
the blades throughout the turbine nearly touch the drum and case 
respectively. 
To form some idea of the forces at work in a turbine we should 
consider, with approximate accuracy, that the steam flows through 
the turbine with a force about ten times as great as that of the 
strongest hurricane; and though the force acting on each blade is 
small, perhaps only a few ounces, or in the largest only a few pounds, 
yet in the aggregate the force is great and can propel large ships or 
drive large dynamos. 
The important factors upon which the proportions of the turbine 
are based are the pressures, velocities and percentages of moisture in 
the steam, as it gradually expands from turbine row to turbine row. 
The blades of the turbine are made of rolled and drawn brass, 
well shaped, and polished so as to reduce the frictional losses in the 
steam to a minimum. The steam enters all round the shaft and first 
traverses the shortest blades on the smallest drum, then through 
larger and larger blades set on larger and larger drums, and so on 
till as it leaves the last blades it is expanded about 100-fold in vol- 
