Figure 63. — Gramme's first commercial dy- 

 namo for an arc ligiit. From Chronique de 

 rindustrie, April 12, 1873, PP- 86, 87, April 

 30, 1873, p. 99. 



cally, and instead of leaving the magnetic circuit open 

 at the ends, he completed the circuit by placing 

 cast-iron plates across the top and bottom of the 

 electromagnets. He provided for the gap in the 

 magnetic circuit in which the armature rotated by 

 leaving a space in the middle of each of the cores of 

 the electromagnets where there were no turns of 

 the field coils. Crescent-shaped pole-pieces were 

 attached to this bare area so as to shunt the magnetic 



field from one electromagnet to the other and thereby 

 pass through the armatures. The armatures were 

 mounted on a common axis perpendicular to that 

 of the electromagnets and they rotated between 

 the concave faces of the pole-pieces. One of the 

 armatures produced the current for the electromagnets 

 of the other armatures, and brushes of silver-plated 

 copper wire collected the current induced in them. 

 The generators were made in two forms, one of low 



PAPER 30: DEVELOPMENT OF ELECTRICAL TECHNOLOGY IN THE 19TH CENTURY: III 



381 



