416 



CHAPTER XX 



sionally high-speed engines making up to 200 r.p.m. are found. The first 

 mention of electric drive is found in Watt's patent (2944, 1883) ; but its 

 introduction is largely due to Williamson's patent (21262, 1896). In this 

 design the field magnets forming the stationary part of the motor are attached 

 to the inner stationary spindle, the armature being connected to the outer 

 rotating spindle. In electric drive, as now carried out, the motor is mounted 

 rigidly, and communication to the rotating spindle is made by a friction 

 clutch or by flexible bearings. Water drive for centrifugals is due to Laidlaw 

 and Matthey (patent 17101 of 1895), who attached a Pelton wheel to the 

 rotating spindle. This method of drive has been very largely adopted. 

 In referring to electric and water drive, it must not be forgotten that 



FIG. 263 



FIG. 264 



in nearly all cases the steam prime mover stands behind the motor whether 

 electric or water. 



In this case their principal difference is that in motor drive each machine 

 has its individual motor, whereas with the older system it is a case of group 

 drive from one larger motor. In discussing the centrifugal machine, it is 

 shown that the power used over the cycle varies very largely from a minimum 

 of zero when stopping to a maximum when accelerating. With individual 

 drive, whether electric or fluid pressure, it is necessary to exaggerate the size 

 of the motor to supply ample power during the acceleration, or otherwise to 

 prolong this period unduly, thus cutting down the capacity of the machine. 

 The water-driven machines of Watson, Laidlaw & Co., Ltd., are supplied 

 with two jets, which operate during acceleration, one being automatically 

 shut off when speed is attained. Similarly, the electric-driven machines 



