Similar farms were used in America until Ralph undertook their study and approached the subject from a scientific angle. One of his first efforts was to obtain greater heat for these huge hothouses. One of these hothouses is about three miles long and the same width. Ralph took the existing hothouses, which were simply oblong steel and glass boxes, and built a second hothouse box covering each of them, thus creating a double-walled, air-locked hothouse. The second glass-paneled wall was about two feet inside the outer one. This left dead air locked between the walls, and as air is a poor heat conductor, the heat in the hothouse was retained longer, particularly during a cold night. Ralph and Alice left early in the morning, winging their way in an aeroflyer toward northern New York, where there were many Accelerated Plant Growing Farms. When the farms came into view, the entire country below, so far as the eye could see, appeared to be dotted with the glass-covered roofs of the plants, reflecting the sunlight and affording an unusual sight. Alice marveled at their number, for while she had seen some of these farms in Europe, she had never seen so many grouped together of such immensity. Within a few minutes, they landed near one of the giant hothouses. The manager led them inside of the farm labeled No. D1569. D1569 was exclusively a wheat growing farm. Where Mother Nature used to grow one crop of wheat a year, Ralph's latest Accelerator made it possible to grow four, and sometimes five crops a year. In the old-fashioned European farms such as Alice knew, only two crops could be grown. "How is it possible," she asked, "that you can obtain three more crops a year than we do in Europe?" "In the first place," said Ralph, "it may be taken as an axiom that the more heat you supply to plant growth, the quicker it will grow. Cold and chilly winds retard plant growth. Electricity and certain chemicals increase the ratio of growth, a fact that has been known for many centuries. It is, however, the scientific application of this knowledge that makes it possible to raise five crops a year. The European farms use only the heat of the sun to stimulate plant growth, but during the night, when the temperature drops, growth is practically nil. "Notice that the top and sides of our hothouses have two walls. In other words, one hothouse is built within another. The air locked between the two hothouses is an excellent heat insulator and even though the sun is low at 4 o'clock, the temperature is practically unchanged in the hothouse, at 8 or 9 o'clock in the evening. Even in the winter, when the sun sets about 4 o'clock and it is cold, we are able to store up enough heat during the day to keep a high temperature as late as 7 and 8 o'clock. If we did nothing between the hours of 8 in the evening and 8 in the morning, the temperature would continue to fall to a point where no plant growth would be possible.