122 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
directly connected with the reduced winding space inside 
the slot, which has to take more insulation material. 
The skill of the designer and the quality of the insulation 
material considerably affect the output constant.. 
198. The Greatest Iron. Reluctance.—lIt should be noted 
that the greatest iron reluctance should be placed in the 
field iron, as such a part does not contribute any noticeable 
amount to the losses, but gives the regulation a favorable 
knee or bend on the open cireuit characteristic. This rule 
represents a compromise between the conditions 1 and 2, 
Par. 181. 
199. Choice of Density.—The conditions 2, 3, 4 and 5 are 
more or less affected by the choice of the current and 
magnetic densities, for which the average values are given 
in Pars. 88, 89 and 95. 
200. Dimensions of Pole Are Ratio.—lIt is necessary to 
bear in mind that the conditions 1 and 4 are both affected 
by the ratio between the pole are and pole pitch, for with 
a very large pole are, the leakage becomes great and with 
a very small pole are the economy of the design is 
diminished. 
For alternate pole alternators it has been found that a pole 
arc ratio of % is about the most suitable value. 
201. Details of Slots.—In designing the slots care should 
be taken that the slot insulation and the coil should be 
designed so as to avoid driving the tooth saturation too 
high, or making the width of the tooth too small, so intro- 
ducing mechanical weakness. 
Once the leading dimensions are fixed, the choice of the right 
number and form of slots should receive the consideration 
of the designer. 
With regard to the amount of leakage, it is advisable to 
