910, 1705.
_Solids, their power of inducing combination_, 564, 618.
---- interfered with, 638.
Solubility of gases in cases of electrolyzation, 717, 728.
_Source of electricity in the voltaic pile_, 875.
---- is chemical action, 879, 916, 919, 1741.
Spark, 1360, 1406.
_Spark, electric, its_ conditions, 1360, 1406, 1553.
---- path, 1407.
---- light, 1553.
---- insensible duration or time, 1438.
---- accompanying dark parts, 1547, 1632.
---- determination, 1370. 1409.
_Spark is affected by the_ dielectrics, 1395, 1421.
---- size of conductor, 1372.
---- form of conductor, 1302, 1374.
---- rarefaction of air, 1375.
_Spark_, atmospheric or lightning, 1464, 1641.
----, negative, 1393, 1467, 1482, 1484, 1502.
----, positive, 1393, 1448, 1467, 1482, 1484, 1502.
----, ragged, 1420, 1448.
----, when not straight, why, 1568.
----, variation in its length, 1381.
----, tendency to its repetition, 1392.
----, facilitates discharge, 1417, 1553.
----, passes into brush, 1448.
----, preceded by induction, 1362.
----, forms nitric acid in air, 324.
----, in gases, 1383, 1421.
----, in air, 1422.
----, in nitrogen, 1422, 1463.
----, in oxygen, 1422.
----, in hydrogen, 1422.
----, in carbonic acid, 1422, 1463.
----, in muriatic acid gas, 1422, 1463.
----, in coal-gas, 1422.
----, in liquids, 1424.
----, precautions, 958, 1074.
----, voltaic, without metallic contact, 915, 956.
---- from single voltaic pair, 1050.
---- from common and voltaic electricity assimilated, 334.
----, first magneto-electric, 32.
---- of voltaic electricity, 280.
---- of common electricity, 333.
---- of magneto-electricity, 348.
---- of thermo-electricity, 349.
---- of animal electricity, 358.
----, brush and glow related, 1533, 1539, 1542.
Sparks, their expected coalition, 1412.
Specific induction. _See_ Induction, specific, 1252.
_Specific inductive capacity_, 1252.
----, apparatus for, 1187.
---- of lac, 1256, 1270, 1308.
---- of sulphur, 1275, 1310.
---- of air, 1284.
---- of gases, 1283, 1290.
---- of glass, 1271.
_Spermaceti_, its conducting power, 1240, 1323.
----, its relation to conduction and insulation, 1322.
Standard of direction in the current, 663.
State, electrotonic, 60, 231, 242, 1114, 1661, 1729.
Static induction. _See_ Induction, static.
_Sturgeon_, his form of Arago's experiment, 249.
----, use of amalgamated zinc by, 863, 999.
_Sulphate of soda_, decomposed by common electricity, 317.
----, electrolytic intensity f