Northern Europeans spend a lot of time in their cold and cloudy winters planning their summer holidays. They are proud of their healthy color when they return home after the holiday. But they also know that a certain amount of sunshine is good for their bodies and general health. In ancient Greece people knew about the healing  powers of the sun, but this knowledge was lost. At the end of the nineteenth century a Danish doctor, Niels Finsen, began to study the effect of sunlight on certain diseases, especially diseases of the skin. He was interested not only in natural sunlight but also in artificially   produced rays. Sunlight began to play a more important part in curing sick people. A Swiss doctor, Auguste Rollier, made full use of the sun in his hospital at Lysine. Lysine is a small village high up in the Alps. The position is important: the rays of the sun with the greatest healing power are the infra-red   and ultra-violet   rays; but ultra-violet rays are too easily lost in fog and the polluted air near industrial towns. Dr. Roller found that sunlight, fresh air and good food cure a great many diseases. He was particularly successful in curing certain forms of tuberculosis with his "sun-cure". There were a large number of children in Dr. Roller's hospital. He decided to start a school where sick children could be cured and at the same time continue to learn. It was not long before his school was full. In winter, wearing only shorts, socks and boots, the children put on their skis after breakfast and left the hospital. They carried small desks and chairs as well as their school books. Their teacher led them over the snow until they reached a slope which faced the sun and was free from cold winds. There they set out their desks and chairs, and school began. Although they wore hardly any clothes, Roller's pupils were very seldom cold. That was because their bodies were full of energy which they got from the sun. But the doctor knew that sunshine can also be dangerous. If, for example, tuberculosis is attacking the lungs, unwise sunbathing may do great harm. Today there is not just one school in the sun. There are several in Switzerland, and since Switzerland is not the only country which has the right conditions, there are similar schools in other places. Dr Roller set up a "sun-cure" school probably for the reason that   _  .
most children could stay in his hospital children could study while being treated the school was expected to be full of pupils the school was high up in the mountains