. Practical electricity in medicine and surgery. Fig. 35. Fig. 36. we have, by KirchhofFs first law, calling G the current throughthe galvanometer, and iJthat through the battery, #= Ca+ C4> G = Gl - C2, G=Ci — C3 From the second law, we obtain in the circuits ABC,BCD, etc., A-B _B-D _A-C C-D V 1 ~ > ^2 _ ~ > °3 _ -r, ) ^i R, R, i?. R* K R From these equations we can eliminate Clt Co C8i Cti andwe finally obtain the relation r -^3 By — -^1 -^4 ° _ (iJ, + R3) (R2 + Bt)+K (R, + R2 + R3 + Rt) But the bridge is always used under the condition that thegalvanometer-current shall be zero; he
. Practical electricity in medicine and surgery. Fig. 35. Fig. 36. we have, by KirchhofFs first law, calling G the current throughthe galvanometer, and iJthat through the battery, #= Ca+ C4> G = Gl - C2, G=Ci — C3 From the second law, we obtain in the circuits ABC,BCD, etc., A-B _B-D _A-C C-D V 1 ~ > ^2 _ ~ > °3 _ -r, ) ^i R, R, i?. R* K R From these equations we can eliminate Clt Co C8i Cti andwe finally obtain the relation r -^3 By — -^1 -^4 ° _ (iJ, + R3) (R2 + Bt)+K (R, + R2 + R3 + Rt) But the bridge is always used under the condition that thegalvanometer-current shall be zero; hence, G = 0, and there-fore B3 R2 = R1Ri . or, R2 RA 42 PRACTICAL ELECTRICITY IN MEDICINE AND SURGERY. It follows, therefore, that if we know the value, in anysystem of units, of one of the resistances, Ru R^ R3, or Ri, an(i tneratio of any two of the remaining three, we can determine thevalue of the other at once in the same system of units. Thus,suppose Ave know that Rt = 10 units, and suppose, further, wefind by actual experiment that R
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