The temperature of interplanetary space is probably very low. Of this Professor Ball says, "What this may be is a matter of some uncertainty, but from all the evidence available it seems plain that we may put it at not less than three hundred degrees below zero;" and the same author adds, "The temperature is taken to be sixty-four degrees below zero, being presumably that at the confines of the atmosphere." Whatever the temperature of space, or its variations, may be, the passage of the planetary electricity through the condensed hydrogen envelope of the sun will produce great changes in the heat of that body and of the solar core within. While with a small electrolytic apparatus we find no special differences of temperature in the gases, with large quantities of electricity, driven at a high potential, we find that a new and startling result ensues. Something of this sort is seen in the operation of electric arc-light lamps, now in common use, in which two slightly separated carbon points are traversed by a current of considerable potential. The current is driven across the intervening space between the points, carrying with it an atmosphere of disintegrated carbon, through which the electricity is carried at its highest speed, and a most brilliant light is produced. In "Electricity in the Service of Man," page 151, it is said, "We may conclude from this that the current does not cease when the arc of light is formed. The resistance of the arc seems to be only very slight; in fact, the current must be conducted by it." Of the structure and constitution of the luminous electrosphere, or arc, produced in these lamps, "Professor J. A. Fleming," says the Scientific American, "has shown that the well-known color of the light of the electric arc from carbon points is due to the incandescence of the carbon filling the space between the positive and the negative rods. The true arc is here, and exists in a space filled with the vapor of carbon, which has a brilliant violet color. Examined by the spectroscope, the central axis of the carbon arc gives a spectrum marked by two bright violet bands. Outside this is an aureole of carbon vapor of yellow or golden color. The electrical strain of the arc occurs chiefly at the surface of the crater which forms at the end of the positive rod, where, in fact, the principal work of generating light is done; for eighty per cent. of the total light of the arc comes from the incandescent carbon at this place. Thus, in a sense, the arc light is mainly an incandescent light, the effect being produced by the layer of carbon which is being constantly evaporated at an extremely elevated temperature. Hence the light of the carbon arc is not, and can never be, white, as it is sometimes described as being, but must always be tinted violet by the carbon vapor normally present between the rods."