THOMAS ROOKE. : XCIII, 
recently that the principal objection to the centrifugal 
pump, namely its inefficiency, has been largely remedied. 
This improved pattern somewhat resembles an inverted 
water turbine, and lifts of 250 to 300 feet are attainable 
by a single impeller, with an efficiency of 65 to 75%. For 
higher lifts, two or more impellers are placed in series, the 
number used depending on the speed of the motor, the lift 
etc. The pumps can also be arranged in a cascade, and 
excessive pressures on packing glands avoided. 
With the introduction of polyphase electric currents, the 
motor has also been greatly simplified, the commutator 
abolished, and the voltage which can safely be applied 
greatly increased. These improvements are of especial 
value in decreasing the attention required by the plant and 
increasing the efficiency of operation at great distances. 
Such a plant can be operated and controlled from a distance, 
is exceedingly small and portable for the duty it will per- 
form and requires very little protection. For many ordinary 
purposes, for mining work, and even in power houses using 
steam, electric pumps have replaced steam pumps, and it 
has been found that their higher efficiency has justified the 
greater first cost and the double conversion of power. In 
mining work the saving effected by electric pumps, has, 
under many conditions been remarkable. Centrifugal 
pumps can also be regulated very simply by means of the 
delivery valve, and the loss of efficiency arising from 
throttling the delivery is not nearly so great as might be 
supposed. If the delivery pipe is throttled, the power 
taken by the motor is also decreased, and if the delivery is 
closed entirely, the impeller churns but does not give rise to 
excessive pressure, whilst the motor absorbs a very much 
smaller power than is required when water is being raised. 
Irrigation works by means of electrically operated pumps 
are now in use by the Kern County Land Company of Cali- 
