action, 822, 869, 960. ——­, ——­, general principles of, 822, 862. ——­, ——­, in chloride of lead, 815. ——­, ——­, ——­ silver, 813. ——­, ——­, in hydriodic acid, 767, 787. ——­, ——­, iodide of lead, 802, 818. ——­, ——­, muriatic acid, 758, 786, ——­, ——­, protochloride of tin, 819. ——­, ——­, water, 732, 785, 807.  Degree in measuring electricity, proposal for, 736. De la Rive on heat at the electrodes, 1637. ——­, his theory of electro-chemical decomposition, 489, 507, 514, 543. Dielectrics, what, 1168. ——­, their importance in electrical actions, 1666. ——­, their relation to static induction, 1296. ——­, their condition under induction, 1369, 1679. ——­, their nature affects the brush, 1455. ——­, their specific electric actions, 1296, 1398, 1423, 1454, 1503, 1560.  Difference of positive and negative discharge, 1465, 1480, 1485.  Differential inductometer, 1307. Direction of ions in the circuit, 962. ——­, the electric current, 563. ——­, the magneto-electric current, 114, 116. ——­, the induced volta-electric current, 19, 26, 1091.  Disruptive discharge, 1359, 1405. See Discharge, disruptive. Discharge, electric, as balls of fire, 1641. ——­, of Leyden jar, 1300. ——­, of voltaic battery by hot air, 271, 274. ——­, ——­ points, 272. ——­, velocity of, in metal, varied, 1333. ——­, varieties of, 1319. ——­, brush, 1425. See Brush. ——­, carrying, 1562. See Discharge, convective. ——­, conductive, 1320. See Conduction. ——­, dark, 1444, 1544. ——­, disruptive, 1359, 1405. ——­, electrolytic, 1343, 1622, 1704. ——­, glow, 1526. See Glow. ——­, positive and negative, 1465. ——­, spark, 1406. See Spark, electric. Discharge, connective, 1442, 1562, 1601, 1623, 1633, 1642. ——­, in insulating media, 1562, 1572. ——­, in good conductors, 1603. ——­, with fluid terminations in air, 1581, 1589. ——­, ——­ liquids, 1597. ——­, from a ball, 1576, 1590. ——­, influence of points in, 1573. ——­, affected by mechanical causes, 1579. ——­, ——­ flame, 1580. ——­, with glow, 1576. ——­, charge of a particle in air, 1564. ——­, ——­ oil of turpentine, 1570. ——­, charge of air by, 1442, 1592. ——­, currents produced in air, 1572, 1581, 1591. ——­, ——­ oil of turpentine, 1595, 1598. ——­, direction of the currents, 1599, 1645. ——­, Porrett’s effects, 1646, ——­, positive and negative, 1593, 1600, 1643. ——­, related to electrolytic discharge, 1622, 1633. Discharge, dark, 1444, 1544, 1560. ——­, with negative glow, 1544. ——­, between positive and negative glow, 1547. ——­, in air, 1548. ——­, muriatic acid gas, 1554. ——­, coal gas, 1556. ——­, hydrogen, 1558. ——­, nitrogen, 1559. Discharge, disruptive, 1405. ——­, preceded by induction, 1362. ——­, determined by one particle, 1370, 1409. ——­, necessary intensity, 1409, 1553. ——­, determining intensity constant, 1410. ——­, related to particular dielectric, 1503. ——­, facilitates like action, 1417, 1435, 1453, 1553. ——­, its time, 1418, 1436, 1498, 1641. ——­,