286 ELECTRICAL MEASUREMENTS 



coils T has a resistance of 1 ohm, and the sliding terminals 

 T l and T\ are mechanically connected so that if T t is shifted 

 to the right, T\ is shifted an equal number of coils to the left. 

 The resistances of both paths between the terminals T t and 

 T\ are thus kept constant. 



As all the coils in decades II and III and all the compensating 

 coils in II' and III' are alike, the resistances of both the left- 

 and the right-hand branches of the circuit are independent of 

 the positions of T n and T m . 



The two sliding contacts on decades IV and the compensating 

 coils IV are mechanically connected so that they must move 

 together, as are the two on decade Fand its compensating coils V. 

 If the contact in decade IV is set on a terminal having a certain 

 number, then automatically the contact in group IV is set on the 

 terminal of the same number, and similarly with V and V. The 

 group of coils IV, consists of a 1-ohm coil ( 1.0 in group I), 

 shunted by a variable resistance which consists of a fixed portion 

 81.64co, and a variable part included between 1 and the posi- 

 tion of the sliding contact. The coils in the variable portion 

 of IV are 



Between Ohms Between Ohms 



-1 and 8.264 4 and 5 30.30 



Oandl 10.101 5 and 6 45.41 



1 and 2 12.626 6 and 7 75.80 



2 and 3 16.234 7 and 8 151.51 



3 and 4 21.645 8 and 9 454.54 



9 and 10 



In the group IV the order is reversed, that is, the coil having 

 a resistance of 8.264 ohms is between contacts 9 and 10. The 

 resistances are given these particular values in order that, 

 when the contact in IV is moved one number, the resistance 

 between T l and T n may always be altered by a definite amount, 

 0.0011 ohm, which is }{QQ of the alteration which would be 

 obtained by moving T n one number. For instance, if the decade 

 contact is on number 4, the resistance of group IV is 



i = - 99342 - 



When it is set oh number 5, this becomes 



*- = - a " 452 - 



