124 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
and the surfaces inside the ventilating ducts, of similar 
expression as the two side faces. 
205. Temperature Rise in Stationary Armatures.— 
For the calculation of temperature rise in the stationary 
armature, the following formula gives good results: 
WwW : 
i items 0 77 (40) 
where W =th: total amount of the armature losses in 
watts ; 
O,=the value of the cooling surface in square 
inches, calculated as shown in Para- 
graph 204; and 
T, = the temperature rise in Fahrenheit degrees. 
In most cases the application of ventilating ducts every 
3 to 4 inches of iron length will be found sufficient, pro- 
viding that the width of such a duct is not less than 0.5 
inch, and that there is free access left for the air to pass 
through. 
206. Temperature Rise in Rotating Magnet Wheels. 
The cooling conditions in a rotating magnet wheel are 
naturally very favorable, and for average peripheral 
speeds, a specific cooling surface of 0.75 to 1 square inch 
per watt loss dissipated in heat, will be sufficient to keep 
the temperature rise within moderate limits. 
The following formula provides a satisfactory method for 
checking the temperature rise: 
Wn 
T= KX O, (10.0087) "7 | 
in which W,, =the energy loss in watts, which is equal 
to the excitation energy consumed in 
the magnet coils; 
O., =the cooling surface composed of the ex- 
ternal cylindrical surface of the coils, 
and the two sectional areas of the pole 
cores, all measured in square inches; 
