DIRECT-CURRENT DYNAMOS AND MOTORS. 
39 
higher, the larger the output of the machine, and the 
greater the number of poles. In dynamos with smooth- 
core armatures, the densities are made greater than in 
those with toothed cores; and in a machine having 
wrought iron or steel polepieces, the density can be chosen 
about 50 per cent. higher than in a similar machine with 
cast iron poles. 
Suitable average values of B, for ordinary dynamos and 
motors are given in Table 16. 
TABLE 16. 
AVERAGE FIELD DENSITIES FOR DYNAMOS AND MOTORS, 
IN LINES PER SQUARE INCH. 
Bipolar Dynamos. Multipolar Dynamos, 
Capacity 
RS Smooth Armature.|Toothed Armature.|Smooth Armature.|Toothed Armature. 
K. W. 
CastIron| Steel (Cast Iron}; Steel |CastIron| Steel (|CastIron| Steel 
Pole- Pole- Pole- Pole- Pole- Pole- Pole- Pole- 
pieces. | pieces, | pieces. | pieces. | pieces. | pieces. | pieces. | pieces 
.1 | 10000] 15000 8000 | 12000 | 14000 | 20°00} 12000) 18000 
.25} 12000] 18000 | 10000} 15000 | 16000 | 24000 | 14000 21000 
.56 | 14000] 20000 | 12000} 18000} 18000] 27000 | 16000 | 24000 
1 15000 | 22000 | 13000} 19000 | 19000} 28000 | 17000 | 25000 
2.5 | 16000; 24000 | 14000 | 20000 | 20000 | 29000} 18000 {| 26U00 
5 17000 | 25000 | 15000 | 22000 | 21000 | 30000} 19000} 28000 
7.5 | 18000} 26000; 16000 | 24000 | 22000} 82000! 20000 | 380000 
10 19000 | 28000 |} 17000 | 25000 | 24000 | 35000} 21000) 38200u 
25 20000 | 30000} 18000 | 27000 | 26000 | 38000 | 22000) 35000 
50 22000 | 33000 | 20000 | 80000 | 28000} 41000 |} 23000 | 388000 
100 | 24000 | 36000 | 22000 | 38000 | 30000 |; 44000 | 25000 | 40000 
200 27000 | 40000 | 24000 | 36000 | 82000 | 47000 | 27000 | 42000 
300 80000 | 45000 | 27000 | 40000 | 35000} 50000 | 29000 | 44000 
500 deere Ress Tee iwes 88000 | 58000} 31000 | 46000 
1000 ‘ ‘tials 41000 | 56000 | 83000 | 48000 
2000 : 45000 | 60000 | 85000 | 50000 
If a strong magnetic field is desired for the purpose of pre- 
venting, or diminishing, the distorting effect of armature 
reaction, values of the gap induction about 20 to 30 per 
cent. in excess of those given in the above table are 
usually taken. 
