The entire expanse, twenty kilometers square, was covered with glass. Underneath the heavy plate glass squares were the photo-electric elements which transformed the solar heat _direct_ into electric energy. The photo-electric elements, of which there were 400 to each square meter, were placed in large movable metal cases, each case containing 1,600 photo-electric units. Each metal case in turn was movable, and mounted on a kind of large tripod in such a manner that each case from sunrise to sunset presented its glass plate directly to the sun. The rays of the sun, consequently, struck the photo-electric elements always vertically, never obliquely. A small electric motor inside of the tripod moved the metal case so as to keep the plates always facing the sun. In order that one case might not take away the light from the one directly behind it, all cases were arranged in long rows, each sufficiently far away from the one preceding it. Thus shadows from one row could not fall on the row behind it. At sunrise, all cases would be almost vertical, but at this time very little current was generated. One hour after sunrise, the plant was working to its full capacity; by noon all cases would be in a horizontal position, and by sunset, they again would be in an almost vertical position, in the opposite direction, however, from that of the morning. The plant would work at its full capacity until one hour before sunset. Each case generated about one hundred and twenty kilowatts almost as long as the sun was shining, and it is easily understood what an enormous power the entire plant could generate. In fact, this plant supplied all the power, light, and heat for entire New York. One-half of the plant was for day use, while the other half during daytime charged the chemical gas-accumulators for night use. In 1909 Cove of Massachusetts invented a thermo-electric Sun-power-generator which could deliver ten volts and six amperes, or one-sixtieth kilowatt in a space of twelve square feet. Since that time inventors by the score had busied themselves to perfect solar generators, but it was not until the year 2469 that the Italian 63A 1243 invented the photo-electric cell, which revolutionized the entire electrical industry. This Italian discovered that by derivatives of the Radium-M class, in conjunction with Tellurium and Arcturium, a photo-electric element could be produced which was strongly affected by the sun's ultra-violet rays and in this condition was able to transform heat _direct_ into electrical energy, without losses of any kind. After watching the enormous power plant for a time Alice remarked: "We, of course, have similar plants across the water but I have never seen anything of such magnitude. It is really colossal. But what gives the sky above such a peculiar black tint?"