the greater the amount of electricity in the air." Referring to the sparking discharge, it is said, page 75, "The density of the air, however, has to be taken into account; the sparking distance is lessened in denser air, and becomes greater when the atmospheric pressure is diminished. Not only the density, but also the chemical composition of the medium influences the sparking distance. Faraday found the distances considerably less in chlorine gas, but twice as long in hydrogen gas as in air." Page 74, "The sparking distance increases at a somewhat greater rate than the difference of potential of the discharging bodies.... When the sparking distance becomes very great ... it is proportional to the difference of potential." Page 91, "There is a difference of potential between the earth and points in the air above. In fine weather the potential is higher the higher we go, increasing usually at the rate of twenty to forty volts for each foot." It will be seen that, continued upward at this rate, the increased electrical pressure for each mile of elevation would be between 100,000 and 200,000 volts, or for each one hundred miles more than 10,000,000 volts; and at an altitude of one thousand miles, if carried so far, the potential would be between one and two hundred million volts, an electrical pressure quite inconceivable to us. Such a potential in currents of enormous quantity continually flowing from the earth to the sun would certainly decompose any aqueous vapors condensed around these bodies. But the question at once arises, What reason is there to suppose that such currents could possibly flow between the earth and the sun, across that vast intervening region of space, a distance of more than 90,000,000 miles? And would not the resistance to such currents in transit be so enormous that the entire potential, however great, would have been practically lost long before reaching the sun? To this there is a complete and irrefutable answer, not based upon any abstract theory, but upon established fact. It is an absolute certainty that electrical currents of enormous quantity and high potential are constantly passing between the earth and the sun, and that these currents have so free a passage--far more free than through any metallic circuits that we know of--that they pass over this enormous distance absolutely without appreciable resistance. We may note in this connection the well-known facts, now being largely utilized, though the art is still in its infancy, of telegraphing and transmitting all sorts of electrical currents over large distances without wires or any conductors, except those furnished by nature.