“Indeed they have not,” he answered, “and they are very unlikely ever to find out how to do it unless instructed by us; and that will never be till the Lunarians become lunatics. The new power that has been developed and already brought into considerable use and which will soon become a substitute for all others and endure as long as the earth is habitable is simply sunlight; and the discovery that is to prove by far the most valuable ever made by your race is the direct conversion of its force into electricity, which can as you know be conveyed hundreds of miles and applied to any sort of machinery required. When coal is used to produce electricity, the process is after all an indirect way of utilizing the force of the sun’s rays. Ages ago these rays created the vegetation that afterwards became coal, and in burning the coal now, the force of the sun’s rays consumed in its production is again brought into action in heating the water, that expands into steam that drives the engine, that turns the dynamo, that creates the electric current. It was seen long ago that if some process could be devised by which the force of the sunlight could be consumed in the creation of electricity directly, the suns rays of to-day could be utilized in the production of power instead of using up the coal that was produced by them in former ages. It was discovered in your day that sunlight falling upon the metal selenium is turned in part into electricity. Acting on this hint your scientists experimented with that metal and others, and tried hundreds of combinations and alloys. They have discovered many compounds that possess this property, which is found to depend on the sizes and shapes of the spaces between the molecules of the metal. The impact of the undulations of the ether that give rise to light, striking into the ether confined in these peculiarly shaped spaces impart to it the sort of motion these shapes make it competent to take, which is the new form of motion, electricity. They were largely assisted and guided in their investigations by spectrum analysis. The apparatus for the production of electricity in this way is necessarily of large dimensions presenting large surface to the sun, and as yet is rather expensive, but once made, it lasts forever and produces electricity whenever the sun shines. Improvements are constantly being made that reduce the cost and increase the efficiency. These machines are arranged to turn automatically, a certain face to the sun, revolving on a horizontal plane diurnally and changing their declination vertically to follow the north and south movement of the sun through the seasons. The electricity is transmitted to storage batteries and a surplus thus accumulated during sunshine to be used at night and in cloudy weather or carried off to be used elsewhere. These machines yield especially good results in tropical latitudes and in localities where clear weather