4. Scientists predict that the world's known oil resources will run out early in the next century. But long before then the world will have to decide on its priorities. Can we afford to use so much of our limited petroleum supplies for private motoring? Should airlines compete on similar routes allowing planes to fly long distances with empty passenger seats? What alternative energy resources can be developed?

5. There is an old English saying, "Necessity is the mother of invention," which means that when you are faced with a need you will discover some way of fulfilling it. Already scientists are proposing some fascinating solutions. There is one suggestion that the wheeled traffic and the footsteps of crowds walking the streets in major cities could generate energy. One company has presented an idea in which metal strips inserted in pavements and roads operate fly wheels by means of a piston action using hydraulic fluid. They say the human and wheeled traffic in a busy city center could provide enough energy to light the streets of an entire town or power the heating system for a hospital or school. Some people are developing sophisticated versions of the windmill. Engines can run on alcohol, so surplus sugar cane could be used to produce energy. An air ship powered by energy from the sun has been suggested. Such "sun ship" would have a large enough surface area to carry the enormous number of solar cells necessary to move any appreciable load. Such "sun ship" might travel at over one hundred kilometers an hour. In such circumstances, of course, the tropical parts of the world would have a head start in the race to find new energy sources.