It has already been mentioned that the stratified discharge can be obtained by a single discharge of the primary current of an inductive coil, however long may be the vacuum tube through which the discharge is passed. If no addition be made to the battery and no alteration be made in the arrangement of the coil so as to increase or diminish the intensity of the discharge, the stratifications will always present the same appearance and form, occupying the same spaces and positions in the vacuum tube; but if any change be made so as to alter the intensity, then a corresponding alteration will appear in the discharge, the striæ assuming a different shape, and the bright and dark divisions occupying different positions.
In order to try what effect a change of intensity would produce, three separate insulated voltaic batteries, in which the exciting liquid was brine, formed an electric circuit which was completed by two long wires. It was so arranged that the discharge of one, two, or all the three batteries could be separately employed. In order to vary the resistance at pleasure, two tubes 18 inches long containing distilled water and connected at their base were introduced into the circuit. By varying the depth to which the terminal wires of the circuit were plunged into the water, the resistance could be regulated at pleasure, and it was immaterial in what part of the circuit the vacuum tube was introduced provided the circuit was completed.
The first experiments were made with a carbonic acid vacuum tube 20 inches long and 4 inches in diameter. The negative terminal at one extremity of the tube was of aluminium, cup-shaped, about 3 inches in diameter; the positive terminal was a wire of the same metal fused into the other extremity of the tube; the point of the wire and cup were about four inches and a half apart. With this tube and 2,240 cells of the battery the discharge when the resistance was introduced had the appearance of a positive and negative discharge, impinging on and intermingling with each other, without any dark space intervening. Around the negative terminal the luminosity extends to the sides of the tube and tapers to the point of the positive wire. The light round the negative terminal becomes brighter, a dark space appears next to it when the resistance is diminished, and increases as the resistance decreases, by the rolling back of the light in bright clouds to the point of the positive terminal. These changes can be perfectly regulated by the resistance, and various luminous phenomena occur at each stage.
With 2,240 cells distinct sounds were heard in the tube; with the whole battery of 3,360 series the sounds were not heard till a magnet was applied to the striæ, when they again became audible and the striæ were spread over the surface of the tube.
A carbonic acid vacuum tube with platinum terminals fused into the same side far apart was now put into the circuit, the part of the wires that penetrated within the tube being coated with glass up to the carbon balls in which they terminated. When a discharge from all the three batteries passed through the tube, changes occurred in the form and number of the striæ corresponding to the greater or less amount of the resistance offered in the circuit.
At the commencement of the experiments there were 18 inches of water in each of the tubes, which formed the maximum resistance. The wires attached to the terminal wires of the battery were placed inside of these tubes, and as soon as they touched the surface of the water a faint luminous discharge was seen at each ball in the vacuum tube. As the wire attached to the negative end of the battery was slowly depressed, the two luminous discharges appeared to travel towards or attract each other, and at times a portion of the positive luminosity passed over and mingled with the negative; in this state the discharge was extinguished by a magnet.
When the wire was pressed farther into the water a dark space about an inch in length divided the light into two parts, the positive glow being sharply defined, the negative glow having an irregular edge. When the wire had been about three inches deep in the water, the positive and negative glows became more brilliant, and a single clearly defined luminous disc burst from the positive side and occupied the middle of the dark space. When the wire was pressed down till 13 inches of it were in the water, a second luminous disc travelled from the positive side, and then the two luminous discs or striæ occupied the dark space at a little distance from one another. As the wire was pressed more into the water, three parallel luminous striæ appeared, then four, then five, and so on till as many as thirteen or fourteen striped the dark central space. With the full power of the battery, the adjacent disc impinged on the glow that surrounded the negative ball. This disc was of a pale green, those adjacent were reddish, while the negative glow was of a bluish white; minute bright scintillations emanated from the negative ball, while distinct luminous flash discharges took place through the striæ. Thus by the amount of resistance introduced into the circuit, the number of striæ can be regulated, their position fixed, separating or closing up the dark space between the luminous glows round the balls.
In these experiments there is indication of a force emanating from the negative wire. The actual disruption of the particles from the negative terminal also indicates a force, and the disruption is as freely obtained by the continuous discharge of the battery as it is by the intermittent discharge of the induction coil. Besides, when Mr. Gassiot sent discharges from the induction coil through Torricellian vacua, he several times observed that while a cloud-like discharge issued from the positive terminal, a long tongue of the most brilliant blue phosphorescent light emanated from the upper part of the negative terminal, and a brilliant white tongue of light was also seen close to the negative wire: so there is reason to believe that force emanates from both terminals.
Some of the preceding striated discharges ‘present an appearance somewhat analogous with the stationary undulations (or nodes) which exist in a column of air when isochronous progressive undulations meet one another from opposite directions, and on the surface of water by mechanical impulses similarly interfering with each other.’[[11]]
‘May not the dark bands be the nodes of undulations arising from similar impulses proceeding from positive and negative discharges? or can the luminous stratifications which we obtain in a close circuit of the secondary coil of an induction apparatus, and in the circuit of a voltaic battery, be the representations of pulsations which pass along the wire of the former, and through the battery of the latter, impulses probably generated by the action of the discharge along the wires?’