A few degrees can make a big difference when it comes to food storage. Foods can go bad if they get too warm. But for many of the world's poor, finding a good way to keep food cool is difficult. Refrigerators are costly and they need electricity.        Yet spoiled food not only creates health risks but also economic losses. Farmers lose money when they have to throw away products that they can not sell quickly.        But in 1995, a teacher in northernprefix = st1 /Nigerianamed Mohammed Bath Abba found a solution. He developed the "Pot-in-Pot Preservation/Cooling System". It uses two round containers made of clay. A smaller pot is placed inside a larger one.        The space between the two pots is filled with wet sand. The inner pot can be filled with fruit, vegetables or drinks. A piece of wet cloth covers the whole cooling system.        Food stored in the smaller pot is kept from spoiling through a simple evaporation   process. Water in the sand between the two pots evaporates through the surface of the larger pot, where drier outside air is moving.        The evaporation process creates a drop in temperature of several degrees. This cools the inner pot and helps keep food safe from harmful bacteria. Some foods can be kept fresh this way for several weeks.        People throughoutNigeriabegan using the invention. And it became popular with farmers in other African countries. Mohammed Bah Abba personally financed   the first five thousand pot-in-pot systems for his own community and five villages nearby.        In 2000, the Rolex Watch Company ofSwitzerlandhonored him with the Rolex Award forEnterprise. This award recognizes people trying to develop projects aimed at improving human knowledge and well-being.        A committee considers projects in science and medicine, technology, exploration and discovery, the environment and cultural history. Winners receive financial assistance to help develop and extend their projects.        The award is given every two years. The next one will be given in 2008. According to the text, why will the food in the inner pot not go bad?
The temperature is lower than the outside. Both of the pots are made of clay. It is covered with a wet cloth. Drier air is moving outside the pots.