OP ARTS AND SCIENCES. 131 



The Gramme Machine. — This machine weighs about 2,700 pounds, 

 stands 30" high, is 40" long and 34" wide. It is driven by a pulley 

 15" in diameter. The armature moves with very little friction. The 

 field of force coils are flat, and there are four of these, each about 10" 

 long, 3-f" deep, and 22" wide. The armature resistance is 0.129 ohms, 

 the field resistance 0.212 ohms; thus making .341 ohms for the total 

 internal resistance. The total weight of wire in the machine is 483 

 pounds ; or the weight of wire is nearly 18 per cent of the total 

 weight of the machine. 



Siemens Machine, or Heffner von Altenek Machine, built by the 

 Siemens Bros. This machine is 61" in length, 28" in breadth, and 

 12" in height. The armature is nearly 34" long, and 9^" external 

 diameter. It is formed by winding 98 pounds of two insulated wires 

 longitudinally, and in eight divisions, around a thin and hollow brass 

 cylinder. Within this hollow cylinder is a hollow stationary cylinder 

 of cast iron, supported by bearings that pass through the brass cylin- 

 der. The commutator has eight divisions, which are eight sector- 

 shaped sheets of brass insulated from, but attached to, the face of a 

 plate which is outside of one of the bearings of the brass cylinder. 

 Two collectors or brushes trail upon and press against these sectors : 

 these brushes have a bearing so extensive as to short circuit or bridge 

 over the edge of two sectors. The spark of the commutator is quite 

 insignificant. This machine differs from all others in this respect : the 

 armature simply moves a wire through a field of force, and not a soft 

 iron core covered with wire. The resistance of the entire circuit, field 

 of force, connected for conductivity, is .586 ohms. The normal veloc- 

 ity of machine is from 370 to 380 revolutions per minute. 



Wilde Machine. — " This resembles, in some respect, the Hjorth 

 machine of 1855, with the permanent magnet omitted. It has two 

 armature circuits : one with current uniform in direction for the pur- 

 pose of maintaining the magnetism of the field ; and the other for pro- 

 ducing the electric light. The current from this last circuit is a to 

 and fro current, without commutator. 



" The armature wire weighs 28 pounds, and is divided into two cir- 

 cuits ; about 7 pounds of it having a resistance of .454 ohms furnishes 

 the current which maintains the field. The remainder, 21 pounds, 

 having a resistance of .074 ohms, maintains the to and fro current. 

 About 325 pounds of wire are distributed in 24 coils to make up the 

 electro-magnetic field which has a resistance of 2.83 ohms. These coils 

 are 10|" in length and 3£" in external diameter, having soft round 

 cores 2" in diameter. There are 24 armature cores and coils, one half 



