18 W. H. WARREN. 
best examples of turbine work are to be found in Switzer- 
land, where also some of the best turbines installed in 
HKurope have been manufactured. The application of the 
laws of hydraulics to the action of water in simple radial 
or parallel flow turbines being for a long time well under- 
stood, the highest hydraulic efficiency attainable for the 
different types could be easily calculated; the actual effici- 
ency is obtained by multiplying the hydraulic by the 
mechanical efficiency, giving from 795 to 85 per cent., which 
is practically realized to-day with turbines of the most 
-approved design. 
The early turbines were of the radial flow type, but this 
was soon replaced by the parallel flow turbine which on | 
account of its simplicity and cheapness became the standard 
type, but the introduction of electrical transmission requir- 
ing higher speeds and better speed control necessitated a 
different type of turbine. Modern requirements appear to 
indicate the following types as the most suitable according 
to John Wolf Thurso :— 
1. For low heads, up to say 20 feet: Radial inward flow 
turbines of the Francis type with vertical shafts, the 
foundation masonry usually forming the turbine case, 
draft tubes being frequently employed. : 
2. For medium heads, say from 20 to 300 feet, radial ‘in- 
ward flow reaction or Francis turbines with. horizontal 
shafts and concentric or spiral cast iron cases with 
draft tubes. 
3. For high heads, say from 300 feet: Radial outward flow, 
full or segmental feed, free deviation turbines with 
horizontal shafts and cast iron or wrought iron cases, 
frequently with draft tubes, or a modified form of the 
Pelton wheel. 
A large number of turbines are in operation in America 
and Hurope, among which may be mentioned the 5,500’ HP.. 
