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ELECTRICAL EXHIBITION AT PHILADELPHIA. 



ed, embodying improvements in construciioD, 

 in winding the armature, and in the arrange- 

 ment of the field-magnets, all covered by pat- 

 ents issued to Weston, Maxim, Edison, Hous- 

 ton-Thomson, Brush, Wallace, Van Depoel, 

 Bernstein,. Ball, and Daft. All have in com- 

 mon an armature whose founda- 

 tion is wrought-iron, with coils 

 wound parallel to the axis of ro- 

 tation, and mounted so as to be 

 revolved in an intense magnetic 

 field. As the copper wires, dur- 

 ing the revolution, cut the lines 

 of magnetic force, an electric cur- 

 rent is produced. 



Among the modern improve- 

 ments exhibited in connection 

 with this point was a regulator 

 attached to the Houston-Thomson 

 dynamo ; the brushes that collect 

 the current from the commutator 

 are attached to a yoke pivoted 

 on an axis ; a lever from this 

 yoke bears an armature at the 

 end that faces near the pole of a 

 large magnet, which is magnet- 

 ized by the current from the dy- 

 namo. When the current is above 

 the average, the magnets are 

 strong enough to pull the brush- 

 es around the commutator, and 

 away from the point where they 

 would collect the largest amount 

 of electricity, and this tends to 

 bring the current back to the 

 normal. When the current is 

 less than the normal, the magnet 

 is weaker, and the brushes ap- 

 proach the point on the commu- 

 tator where the maximum amount 

 of current is given off. This regu- 

 lator always tends to bring the 

 current back to the normal, and 

 is exceedingly sensitive. Judging 

 from the lamps burning on that 

 circuit, the current must be re- 

 markably steady. The generating 

 armature is globular, and the cop- 

 per wires are wound in three coils 

 around a great circle, intersecting 

 each other with an angle of 33. 

 The ends of these coils are con- 

 nected to six commutator strips 

 on which the movable brushes 

 rest. The commutator revolves 

 in a magnetic field produced be- 

 tween two cylinders, wound so that the two 

 concave ends between which the globular ar- 

 mature revolves are the north and south poles. 

 When the copper wire in the armature cuts 

 the south pole, it produces there a negative 

 current, and at the same time the wire on 

 the other side of the armature is cutting the 

 north pole and producing positive electricity. 

 Instead of having one armature for both kinds 

 of electricity, Ball's unipolar machine had an 



armature for each kind of electricity, one rotat- 

 ing in a magnetic field of north polarity, and 

 the other on the same shaft, rotating in a field 

 of south polarity. Wallace's exhibits were es- 

 pecially interesting from an historical point of 

 view. His old machines, made in 1861, which 



GEKARD LAMP. 



were the first dynamos made in this country, 

 have permanent magnets and a great clumsy 

 armature. The evolution of the present dyna- 

 mo from that is only one of perfection in me- 

 chanical details ; the principle underlying the 

 machine has always been the same. Edison 

 in his large dynamo replaces the copper wires 

 with a strip of copper, which reduces the inter- 

 nal resistance, a very important factor in large 

 plants. The dynamo is the most economical 





