516 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
INDEX TO PART IV. 
PAGE 
Air, striking distance in dry and moist, fig. 9 . . . . . . . . . . . . . . 483-484 
Aurora, height of, figs. 1-3 .. . . . . . . . . . . .. . . . . .. 477-480 
Column of gas, potentials at different nearly aliquot parts of, at various pressures, figs. 13-22 .. 489-499 
Column of gas, evidence of a reversal of current in parts of it during a discharge, fig. 29 .. 510-512 
Complex strata, fig. 12; Plate 35, fig. 9 . . . . . . . . .. .. . . . . 487 
Dark negative space, actinically dark only by comparison with strata, Plate 36, fig. 21 b .. 488-489 
Deposit, mirror-like, during a discharge, fig. 8 .. .. .. . . . . . . . . 482 
Discharge from two separate batteries through the same tube, first in the same and then in a 
contrary direction, fig. 10; Plate 35, figs. 1-6 . . . . .. .. . . .. .. 484-485 
Discharge from two separate batteries through the same tube, crossing each other at right 
angles, fig. 11; Plate 35, fig. 10; Plate 36, figs. 15-20.. .. .. .. .. .. 485-487 
Discharge in large tubes, Plate 35, figs. 11-14 .. .. . . . . . . . . . . 488 
Discharge in miniature tubes, figs. 4-6 . „ . . . . .. . . . . . . . . 481-482 
Eddies in an electric discharge through a vacuum tube, figs. 29-30 . . .. .. 510-514 
Electrical condition of a gas in a vacuum tube in the vicinity of the negative terminal, figs. 23-27 500-505 
Electrometer, modification of the mode of working with, Professor Stokes’, figs. 13-15 .. 489-492 
Electrometer, needle resting-point, determined from consecutive swings, fig. 15 .. .. .. 491 
Luminous spindle, electrical condition of, fig. 28, 1, 2, 3, 4, 5 .„ . . . . . . .. 506-508 
Molecules, freedom of motion of . . . . . . . . .. . . . . . . .. 480-481 
Negative terminal, electrical condition of a gas in the vicinity of, figs. 23-27 .. .. .. 500-505 
Negative ring terminal, potential at the centre and periphery of, fig. 28 .. .. .. .. 506-508 
Occlusion of gas by terminals, figs. 7-8 .. .. .. .. . . . . .. .. 482-483 
Palladio-bydrogen volatile alloy, occlusion of, figs. 7-8 . . . . . . . . . . .. 482 
Ponderable matter necessary for the transfer of electricity . . . . . . . . . . . 480-481 
Potential across a dark space and a stratum respectively, fig. 28, 6 .. . . . . .. 508-510 
Potential at different nearly aliquot parts of a column of gas at various pressures, figs. 13-22 .. 498-499 
Potential at the centre and periphery of negative ring terminal, fig. 28 .. .. .. .. 506-508 
Potential, full, determination of, fig. 16 ., . , .. .. .. . . .. .. 492 
Pressure of least resistance, dependent on the shape and dimensions of vessel, figs. 1, 2, 3 .. 477-481 
Spark, length of, in dry and moist air, fig. 9 .. .. .. .. .. .. .. .. 483-484 
Spindle of light protruding through negative ring terminal, electrical condition of, fig. 28, 1, 2, 
3, 4, 5 .. . 506-508 
Strata, complex, fig. 12; Plate 35, fig. 9 .. .. . . .. .. .. .. .. 487 
Strata produced by separate discharges in opposite directions in the same tube, Plate 35, figs. 1-6 484-485 
Strata produced by separate discharges and crossing each other at right angles, fig. 11; Plate 35, 
fig. 10; Plate 36, figs. 15-20 . 485-487 
Stratum, apparent plasticity of the aggregate assemblage of molecules constituting it, Plate 36, 
fig. 17 . 486 
Stratum, threaded on the negative terminal, Plate 35, fig. 9 . . . . .. . . .. 487 
Two batteries, mutual accommodation of, Plate 36, fig. 15 .. . . .. . . .. •. 486 
Two separate currents in the same tube, first in the same and then in a contrary direction, 
fig. 10; Plate 35, figs. 1-6.. .. . 484-485 
