Mr. R. H. M. Bosanquet on Practical Electricity. 243 



"When the polarity gets reversed from any cause, I call it 

 " reversed." In this case the upper pole-piece attracts the 

 marked end of a compass-needle. 



The directions of currents and rotation deserve some at- 

 tention. 



The machine is driven in the direction opposite to that of 

 the hands of a watch, regarded from the pulley-end. It 

 gives currents in the one or the other direction according as 

 it is "straight" or "reversed." This is obvious; for with 

 reversal of the current both field-magnets and armature are 

 reversed, and the attractions which have to be overcome in 

 doing the work remain the same. 



When a current is sent through the machine from a batteiy, 

 it always turns in the direction opposite to that in which it is 

 driven by the engine ; for whichever way the current goes 

 the attractions are the same as in the former case, and as 

 these are overcome by the engine in that case, it is clear that 

 they tend to turn the machine in the opposite direction to the 

 engine. 



When the machine is driven 

 by a battery, with the hands of 

 a watch from pulley-end, it is 

 necessary so to adjust the brushes 

 that their ends may not -catch 

 in the commutator. I turn 

 up the ends of a spare pair of 

 brushes, and apply them to the 

 commutator in, this manner. 



Otherwise the machine can be caused to turn in its normal 

 direction when driven by a current, by reversing the connex- 

 ions between armature and magnets ; this is made possible 

 by the cutting of the wire above described. The arrangement 

 may be formulated thus: — 



Armatur 



Magnets Magnets 



Terminal Terminal 



The machine is constructed for driving one arc light. 

 Although this is not a matter with which I am directly con- 

 cerned, the normal conditions may be of interest: — 

 R2 



