ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 135 
the iron parts it is necessary to calculate the densities in 
the same, and the magnetic induction in the teeth will 
be especially decisive regarding the length of the armature. 
Par. 218, gives a normal armature fiux of 4.12 x 10° lines 
per pole; the section offered to this flux by the teeth is 
8.75 
equal toS x xr x09 = 2 > x 95x15 x 0.9 = 47 
square inches, with reference to Fig. 6€. 
232. Calculation of Teeth Section.—In machines with 
small or medium sized bore, it will be advisable to cal- 
culate the tooth section at the bottom and at the top part 
of the toothed body. In this particular case o on the 
172.4 
inside periphery = eT ites 2.4 inches; and r=o—s= 
1.5 inches. 
: 59.1 X 3.14 
At the top of the teeth, o= - = 2.57 inches, 
and r—=o—s= 2.57 — 0.9 = 1.67; 
so that the average value of tooth section, with r= 
1.5 + 1.67 8.75 
as — = 1.58, is a x 9.5 x 1.58 x 0.9 = 49 square 
inches with an average magnetic density of 
4.12 x 10° 
= 84,000 lines per square inch. 
49 
233. Value of Iron Loss.—This value is about 20 per cent. 
higher than the usual mean density corresponding to 50 
eycles, but it may be considered a good value, as it does 
not cause more hysteresis and eddy current losses than 
5.5 + 1.25 = 6.75 watts per pound of iron. 
The calculation of the losses in this particular case will 
show that a standard efficiency is easily obtained. 
234. Length of Armature.—The effective iron length of the 
armature = 8.6 inches; to this has to be added about 10 
