488 APPLIED MECHANICS 
about 1865. The hurdy-gurdy was a vertical wheel, having flat radial 
vanes, upon which a jet of water with high ‘velocity impinged. ' 
maximum theoretical efficiency of the hurdy-gurdy is only 50 per ce 
and its actual efficiency from 25 to 35 per cent. a 
The substitution of curved buckets for the flat vanes was the gre 
improvement which converted the hurdy-gurdy into the Pelton wh 
—> 
Fig. 786. 
which the buckets are attached. The jet issues from a nozzle at the end ~ 
of a pipe and strikes against the buckets, as shown. ‘The form of the 
Pelton bucket is shown in Fig. 787, from which it will be seeu that the 
jet is divided by a sharp ridge in % 
the bucket, and is then gradually 
deflected through an angle slightly 
less than 180°. It is necessary to 
make the angle through which the 
jet is deflected less than 180°, in 
order that the returning stream 
may clear the bucket which 
follows. The Doble bucket, shown 
in Fig. 788, is an improvement 
on the Pelton bucket. The im- 
provement consists in making the 
two compartments of the bucket 
of ellipsoidal form, and in cutting 
away a part of the outer lip to 
into action. ¥ 
The disc of the wheel may be of cast-iron or steel, and the buckets 
may be of cast-iron or hard bronze. 4 
Assuming a complete reversal of the jet, it is evident that if the 
velocity of the buckets is half that of the jet the absolute velocity of the 
clear thé jet as the bucket comes | 
