DIRECT-CURRENT DYNAMOS AND MOTORS. 
be made about }inch, whereas in the latter case G-H should 
be either about 4 inch for a ring armature, or about 7 
inch for a drum (compare with Tables 14 and 25). 
The lines BJ and DJ are then drawn vertically downward 
from the points B and D, a distance equal to the length 
of the cores, which, since wrought iron polepieces are 
used, is 9 inches or 13} inches, according to whether 
the armature has a toothed or a smooth core, respectively. 
The diameters IK and .’Z are made equal to Dn, which 
has been found to be 10 inches. In Fig. 25 the toothed- 
core design is shown at the left side of the center line and 
the smooth-core design at the right side, so that a com- 
parison can be made at a glance. 
The yoke of a bipolar machine is usually made of rectangu- 
lar cross-section having a breadth equal to the diameter 
of the cores. Its height JM or JWN should therefore in 
this case be as = %# inches, provided the same material 
is employed as for the cores. The cross-section of the 
yoke is thus made equal to that of the cores, and is kept 
practically uniform throughout; whereas the polepieces 
may be tapered, as shown, so that the middle section at 
HO is about % as large as the core-section, or about 
xX 77.8 
10 = 5 inches 
thick, the divisor 103 being the length of the polepieces, 
which is equal to that of the armature. If the distribu- 
tion of the lines in the air gaps were uniform, only 4 the 
total flux would pass through the section HO; but when 
the field is distorted by armature reaction, the flux in the 
upper half of one of the polepieces may increase to about 
2 of the total amount. 
The radial depth of the armature core required to carry 
the flux @ is: 
vi 5,000,000 
*"~ 2 80,000 xX 103 x .95 
= 34 inches, 
