_Current_ (C).—The Ampère. This is the strength of current sent through a wire having the resistance of 1 ohm at the E. M. F. of 1 volt. _Quantity_ (Q).—The Coulomb. It is the quantity of electricity given by an ampère in a second. One coulomb decomposes ·00142 grain of water. _Heat or Work_ (W).—The Joule, or Volt-Coulomb, is the work done by 1 coulomb in 1 ohm. The work done by any current per second is obtained in ergs by the product of the current into the electro-motive force producing it or W = CE or W = C²R. The Erg is the C. G. S. unit of work. _Power_ (P).—The Watt, 1 ÷ 746 of a horse-power, employed in doing 1 joule of work in 1 second. HP, or the Horse-power, is found by dividing C E by 746, thus (CE)/746 or (C²R)/746 = HP. See also explanation of terms. ELECTRICAL TABLE OF THE BIRMINGHAM WIRE GAUGE FOR PURE COPPER. +---+-----+-----+-------+-------+---------+--------+--------+--------+ |B. |Diam.|Diam.|Area in|Circum.| Pounds | Feet | Feet | Ohms | |W. | in | in |Square | in | per | per | per | per | |G. | In. | mm. |Inches.|Inches.| Mile. | Pound. | Ohm. | 1000 | |No.| | | | | | | | Feet. | +---+-----+-----+-------+-------+---------+--------+--------+--------+ | 1 |·3 |7·62 |·070686|·94248 |1444·0087| 3·662 |8706·843| ·1148 | | 2 |·284 |7·21 |·063347|·89221 |1291·8699| 4·0988|7803·51 | ·1282 | | 3 |·259 |6·58 |·052685|·81367 |1074·5697| 4·9262|6490·09 | ·1540 | | 4 |·238 |6·04 |·044488|·74770 | 907·3683| 5·850 |5580·01 | ·17007| | 5 |·22 |5·59 |·038013|·69115 | 773·045 | 6·83 |4681·1 | ·2136 | | 6 |·203 |5·16 |·032365|·63774 | 657·205 | 8·02 |3985·7 | ·2509 | | 7 |·180 |4·57 |·025447|·56549 | 517·493 | 10·20 |3134·8 | ·3190 | | 8 |·165 |4·19 |·021382|·51836 | 434·861 | 12·14 |2633·7 | ·3797 | | 9 |·148 |3·76 |·017203|·46495 | 349·853 | 15·10 |2119·9 | ·4719 | |10 |·134 |3·40 |·014103|·42097 | 286·651 | 18·44 |1737·0 | ·5757 | |11 |·120 |3·05 |·011309|·37699 | 229·997 | 22·95 |1392·9 | ·7179 | |12 |·109 |2·77 |·009331|·34243 | 189·763 | 27·82 |1149·4 | ·8700 | |13 |·095 |2·41 |·007088|·29845 | 144·144 | 36·63 | 873·1 | 1·1454 | |14 |·083 |2·11 |·005411|·26075 | 110·035 | 47·98 | 665·3 | 1·503 | |15 |·072 |1·83 |·004071|·22619 | 82·790 | 63·77 | 501·5 | 1·9941 | |16 |·065 |1·65 |·003318|·20420 | 67·478 | 78·25 | 408·7 | 2·4466 | |17 |·058 |1·47 |·002642|·18221 | 51·3163|102·89 | 310·8 | 3·2176 | |18 |·049 |1·24 |·001886|·15394 | 38·3486|137·68 | 232·3 | 4·3052 | |19 |·042 |1·07 |·001385|·13195 | 28·1741|187·40 | 170·6 | 5·8599 | |20 |·035 | ·89 |·000962|·10995 | 19·5677|269·83 | 118·5 | 8·4381 | |21 |·032 | ·81 |·000804|·10053 | 16·3574|322·79 | 99·1 |10·094 | |22 |·028 | ·71 |·000616|·08796 | 12·5242|421·58 | 75·8 |13·185 | |23 |·025 | ·63 |·000491|·07854 | 9·9845|528·82 | 60·5 |16·539 |