If direct current is used for distribution, a motor generator set for furnishing alter nating current to the primary of the transformer is required. Any frequency from 60 cycles up is suitable for the operation of these tubes. At low(I. frequencies there is some appreciable variation of the light emitted. One other de vice is necessary for the suitable operation of this form of light and this is known as the regulator. In order to maintain a constant pres sure inside the tube, and such a constant pressure is necessary for its satisfactory operation, there must be some automatic device which will allow a small amount of gas to enter the tube at intervals while it is in operation. The regulator accomplishes this purpose. Fig. 30 shows a diagram of the very simple connections of the system and gives the relative positions occupied by the transformer, tube, and regu lator. Fig. 31 gives an enlarged view of the regulator, a description of which and its method of operation is given as follows: A piece of j-inch glass tubing is supported vertically and its bottom end is contracted into a I-inch glass tube which extends to the main lighting tube.
At the point of contraction at the bottom of the Finch tube there is sealed by means of cement a }-inch carbon plug, the porosity of which is not great enough to allow mercury to percolate through it but which will permit gases easily to pass, due to the high vacuum of the lighting tube connected to the lower end of the plug, and approximately atmospheric pressure above it. This carbon plug is normally com pletely covered with what would correspond to a thimbleful of mercury which simply seals the pores of the carbon plug, and therefore has nothing whatever to do with the conducting properties of the gas in the main tube which produces the light. Partly immersed in the
mercury and concentric with the carbon plug, is another smaller and movable glass tube, the upper end of which is filled with soft iron wire, which acts as the core of a small solenoid con nected in series with the transformer. The action of the solenoid is to lift the concentric glass tube partly out of the mercury, the sur face of which falls and thereby causes the minute tip of the conical shaped carbon plug to be slightly exposed for a second or two.
This exposure is sufficient to allow a small amount of gas to enter the tube, the current decreases slightly, and the carbon plug is again sealed. The process above described takes place at intervals of about one minute when the tube is in operation.
The color of the light emitted by the tube depends upon the gas used in it. The regulator is fitted with some chem ical arrangement whereby the proper gas is admitted to it when the tube is in opera tion. Nitrogen is employed when the tube gives the highest efficiency and the light emitted when this gas is used is yellowish in color. Air gives a pink appearance to the tube and carbon dioxide is employed when a white light is desired.
Table IX gives general data on the Moore tube light. The advantages claimed for this light are: High efficiency, good color, and low intrinsic brilliancy.