APPENDIX I. 



equal and opposite to A, and the other equal to B. In other words, 

 B must be the resultant of the primary field and the armature fielc 1 A. 

 The curve C in Fig. 50 gives the induction in this primary field or 

 as it is also called, the "impressed field," being that field which is 

 impressed on the machine by the supply currents circulating through 

 the field coils. It will be noticed that the resultant field lags behind 

 the impressed field by an angle which is less than a quarter period. 



The working condition of the motor, which has here been investi- 

 gated by means of curves, can also be shown by a clock diagram. Let 

 in Fig. 106, the maximum field strength within the interpolar space 

 (i. e., number of lines per square centimetre at a and b of Fig. 104, 

 be represented by the line O B, and let O I a represent the total am- 

 pere-turns due to armature currents in the bars to the left or the 

 right of the vertical, then O A represents to the same scale as B 

 the maximum induction due to these ampere-turns. We need not 

 stop here to inquire into the exact relation between O l a and O A, 

 this will be explained later on. For the present it is only necessary 

 to note that under our assumption of no magnetic leakage in 

 the machine, O A must stand at right angles to O I a , and there- 

 fore also to O B, and that the ratio between O l a and O A (i. e., 

 armature ampere-turns and armature field) is a constant. By draw- 

 ing a vertical from the end of B and making it equal to O A, we find 

 O C the maximum induction of the impressed field. The total am- 

 pere-turns required on the field magnet to produce this impressed 

 field are found by drawing a line from C under the same angle to 

 C O, as A I a forms with A O, and prolonging this line to its intersec- 

 tion with a line drawn through O at right angles to O C. Thus we 

 obtain O I c , the total ampere-turns to be applied to the field. The 

 little diagram below shows a section through the machine, but in- 

 stead of representing the conductors by little circles as before, the 

 armature and field currents are shown by the tapering lines, the 

 thickness of the lines being supposed to indicate the density of cur- 

 rent per centimetre of circumference at each place. 



95 



