But his fate may be far weirder and more dreadful. Scientists say that as we burn the coal and timber we are still so richly supplied with, we let loose into the atmosphere an ever-increasing volume of carbonic acid gas. Much of this is taken up by plants, but not all. It must increase and eventually poison the breathable air, filling the valleys and mounting slowly to the hilltops, where the last remnants of animal life are striving for existence. The last man will climb higher and higher, but eventually the suffocating invisible flood will reach and drown him. Again, it is said that the earth, as it gets older, is cracking like dry mud. These cracks will increase until at last they will let the waters of the oceans and rivers sink into the fiery center of the globe. Then will occur an explosion so terrible as may startle the inhabitants of neighboring worlds. The last man in this case will probably be some arctic explorer or Eskimo, whom the vast plains of ice around him will save from instant death and leave to grill a few moments till the ice continents are swallowed by red-hot gases and steam. Supposing these earth cracks develop more slowly, they may suck away the water without devastating explosions. Then the last man’s fate will be the worst describable. He will die of thirst. The scene of his death will probably be the great valley in the bed of the Atlantic Ocean, off the Brazilian coast, halfway between Rio Janeiro and the Cape, where now six miles of green water lie between the steamer’s keel and the abysmal slime beneath. There, hopelessly digging in the everdrying mud, he must perish, and leave his bones to parch on a waterless planet. The antarctic polar ice cap has been growing thicker and heavier for uncounted ages. The distance from the south pole to the edge of this ice cap is 1,400 miles. The ice rises steadily from the edge to the center. At that center it cannot be less than twelve miles in thickness--twice as thick as Mount Everest is high. Southern latitudes are growing warmer, and this ice cap is known to be cracking. Suppose it splits. Imagine the gigantic mass of water and ice that will come sweeping up north over the oceans and continents of the earth! Where, then, will the last man breathe his final gasp? High up in the snows of some great range he will perish miserably of cold and starvation, looking down on a huge shallow sea, beneath whose tossing waters will lie the whole of the races of the world. Or, last, and perhaps dreariest fate of all, the human race may outlive other mammals and last until the sun, as some day it must, grows dull and cold, and vegetation dies from the chilled earth. The miserable remnant of earth’s people must then slowly die out after ages of an existence to which that of the Eskimo of to-day is a paradise. HOW CANTILEVER BRIDGES ARE CONSTRUCTED.