XV.  APPENDIX 
ALTERNATING-CURRENT  COMMUTATOR   MOTOR 

78.  Since  in  the  series  motor  and  in  the  shunt  motor  the 
direction  of  the  rotation  remains  the  same  at  a  reversal  of  the 
impressed  voltage,  these  motors  can  be  operated  by  an  alternat- 
ing voltage,   as    alternating-current    motors,   by   making   such 
changes  in  the  materials,  proportioning  and  design,  as  the  al- 
ternating nature  of  the  current  requires.