Place the lamp bank and the ammeter in one side of the power line from the switch to the conductor, and the other end of the conductor to the other side of the power line. Connect the voltmeter across the ends of the cable so as to measure the drop of potential between the ends of the conductor being tested. Close the switch, take simultaneous readings on the voltmeter and the ammeter and calculate the resistance. With the apparatus described a conductor 1 mile long will receive about 2½ amperes and show a drop of about 50 volts. The lamps are inserted as a safety precaution. In no case should the current through the conductor exceed 6 amperes. If the cable has been tested for insulation resistance and all the conductors show high insulation, the lamps are not necessary, provided the cable is at least a mile long. 2. The copper resistance found is reduced to that at 60° F. by multiplying by the coefficient found in the following table with the temperature of the water in the tank at the time of the test as an argument: _Reduction of copper resistance to 60° F._ +--------------+--------++--------------+--------+ | Temperature. | δ || Temperature. | δ | +--------------+--------++--------------+--------+ | _°F._ | || _°F._ | | | 10 | 1.1252 || 55 | 1.0113 | | 11 | 1.1224 || 56 | 1.0090 | | 12 | 1.1196 || 57 | 1.0068 | | 13 | 1.1168 || 58 | 1.0045 | | 14 | 1.1141 || 59 | 1.0023 | | 15 | 1.1113 || 60 | 1.0000 | | 16 | 1.1086 || 61 | .9978 | | 17 | 1.1059 || 62 | .9956 | | 18 | 1.1032 || 63 | .9933 | | 19 | 1.1005 || 64 | .9911 | | 20 | 1.0978 || 65 | .9889 | | 21 | 1.0952 || 66 | .9867 | | 22 | 1.0925 || 67 | .9846 | | 23 | 1.0899 || 68 | .9824 | | 24 | 1.0873 || 69 | .9802 | | 25 | 1.0846 || 70 | .9781 | | 26 | 1.0820 || 71 | .9759 | | 27 | 1.0794 || 72 | .9738 | | 28 | 1.0769 || 73 | .9717 | | 29 | 1.0743 || 74 | .9695 | | 30 | 1.0717 || 75 | .9674 | | 31 | 1.0692 || 76 | .9653 | | 32 | 1.0667 || 77 | .9632 | | 33 | 1.0641 || 78 | .9611 | | 34 | 1.0616 || 79 | .9591 | | 35 | 1.0591 || 80 | .9570 | | 36 | 1.0566 || 81 | .9549 | | 37 | 1.0542 || 82 | .9529 | | 38 | 1.0517 || 83 | .9508 | | 39 | 1.0492 || 84 | .9488 |