OPERATION OF SYNCHRONOUS MOTORS. HUNTING 131 



enon of successive falling out of and falling into synchronism. For 

 instance, Hutin and Leblanc (M. Leblanc, Lumiere Electrique, Vol. 

 XXXIII, p. 227, and F. Geraldy, ibid., Vol. XLVI, p. 652) showed 

 by an experiment that some Ganz motors of the kind excited by 

 commutated currents did not always attain synchronism, but, in cer- 

 tain cases (especially when running without load), assume an oscillatory 

 movement having long periods. These periods can, in such a case, 

 be attributed to slow alternations of the excitation produced by the 

 current-commutator. This is an additional reason for abandoning 

 definitely this kind of excitation. Certain motors also appear subject 

 to slow oscillations, in consequence of the discontinuity of the V-curve 

 produced by the presence of important upper harmonics in their E.M.F. 

 curve, as already noted above (page 103). 



