Electrical measurementsA laboratory manual . . + + . — 945. . + 983. ... Mean . The successive points at which the correction should be appliedare l\ 2^ 3Z etc. 45. Calibration of Bridge Wire — Second Method.^ — Make as many approximately equal resistances as thereare steps in the desired calibration. Let this number ben. Fig. 32 shows ten such resistances. Let them con-nect the mercury cups 1, 2, 3, etc. To insure good con-tact each small resistance should be soldered to a short Cavl Barns, Bulletin U.
Electrical measurementsA laboratory manual . . + + . — 945. . + 983. ... Mean . The successive points at which the correction should be appliedare l\ 2^ 3Z etc. 45. Calibration of Bridge Wire — Second Method.^ — Make as many approximately equal resistances as thereare steps in the desired calibration. Let this number ben. Fig. 32 shows ten such resistances. Let them con-nect the mercury cups 1, 2, 3, etc. To insure good con-tact each small resistance should be soldered to a short Cavl Barns, Bulletin Geological , Xo. 14. RESISTANCE. 79 heavy rod of copper. If L is the length of AC to becalibrated, and / the interval of calibration = 1, Find a point 3Ii on AB having the same potentialas iVi, and JjT. the same as iV^,. This is done by meansof the sensitive galvanometer G. Then exchange wires Nos. L»and II. Find points onAC having the same potential as JSF^^ iV^3, these points M2, The resistance of I. should. Fig. 32. be such that the reading for M^., iff3, etc., shall be a littlesmaller than for ilf^, Jfy, etc. That is, the calibrationdistances set off should overlap a little. Then exchange I. and III. and perform the same oper-ations as before. Continue the process till the conductorI. has been carried along the entire series and finallytakes the place of the last one. The result is to lay offalong the bridge wire distances such that the their ends is the same as between the ends ofconductor I. If the current remains absolutely constant,all these potential differences are equal to each other,and therefore the resistances of the successive lengthslaid off are also equal. They will equal one another ifthe current does not remain constant, provided the rela- 80 ELECTBtCAL MEASUREMENTS. tive resistance of conductor I. to this part of the dividedcircuit remain the same; for any decrease in the currentwill cause a decrease in the be
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