----+--------------+----------+---------+---------+----------+------ | Diameter | | | | | B +-------+------+ Circular | SA | WL | R | C | Mils | MM | mils | | | | ----+-------+------+----------+---------+---------+----------+------ 0000|460.000|11.684|211,600.00|107.219 | 1.56|19,929.700|312.0 000|409.640|10.405|167,805.00| 85.028 | 1.97|15,804.900|262.0 00|364.800| 9.266|133,079.40| 67.431 | 2.49|12,534.200|220.0 0|324.950| 8.254|105,592.50| 53.470 | 3.13| 9,945.300|185.0 2|257.630| 6.544| 66,373.00| 33.631 | 4.99| 6,251.400|131.0 4|204.310| 5.189| 41,742.00| 21.151 | 7.93| 3,931.600| 92.3 6|162.020| 4.115| 26,250.50| 13.301 | 12.61| 2,472.400| 65.2 8|128.490| 3.264| 16,509.00| 8.366 | 20.05| 1,555.000| 46.1 10|101.890| 2.588| 10,381.00| 5.260 | 31.38| 977.800| 32.5 12| 80.808| 2.053| 6,529.90| 3.309 | 50.69| 615.020| 23.0 14| 64.084| 1.628| 4,106.80| 2.081 | 80.59| 386.800| 16.2 16| 50.820| 1.291| 2,582.90| 1.309 | 128.14| 243.250| 11.5 18| 40.303| 1.024| 1,624.30| 0.823 | 203.76| 152.990| 8.1 20| 31.961| 0.812| 1,021.50| 0.5176 | 324.00| 96.210| 5.7 22| 25.347| 0.644| 642.70| 0.3255 | 515.15| 60.510| 4.0 24| 20.100| 0.511| 504.01| 0.2047 | 819.21| 38.050| 2.8 26| 15.940| 0.405| 254.01| 0.1288 | 1,302.61| 23.930| 2.0 28| 12.641| 0.321| 159.79| 0.08097| 2,071.22| 15.050| 1.4 30| 10.025| 0.255| 100.50| 0.05092| 3,293.97| 9.466| 1.0 32| 7.950| 0.202| 63.20| 0.03203| 5,236.66| 5.952| 0.70 34| 6.304| 0.160| 39.74| 0.02014| 8,328.30| 3.743| 0.50 36| 5.000| 0.127| 25.00| 0.01267|13,238.83| 2.355| 0.35 38| 3.965| 0.101| 15.72| 0.00797|20,854.65| 1.481| 0.25 40| 3.144| 0.080| 9.89| 0.00501|33,175.94| 0.931| 0.17 ----+-------+------+----------+---------+---------+----------+------ Important Topics (1) _Galvanometers_: (1) moving magnet, fixed coil; (2) moving coil, fixed magnet, ammeter, voltmeter. (2) _Unit of quantity, coulomb._ (3) _Unit of current, ampere._ (4) _Unit of resistance, ohm._ (5) _Unit of electromotive force, volt._ Exercises 1. How will the resistance of 20 ft. of No. 22 German silver wire compare with that of 10 ft. of No. 22 copper wire? Explain. 2. Where in a circuit is copper wire desirable? Where should German silver wire be used? 3. Explain the action of the ammeter. Why does not the needle or coil swing the full distance with a small current? 4. Why is a telegraph sounder more apt to work on a short line than upon a long one? [Illustration: FIG. 250.--The ammeter is connected in series and the voltmeter in shunt.] 5. Find the resistance of 15 miles of copper telephone wire No. 12. (See table p. 296.)