In the middle of the 17th century, Jan Baptist van Helmont concluded that plants draw life from water. In 1774, Joseph Priestley was experimenting with air and found that plants regenerate the stale air breathed out by animals. Jan Ingenhousz continued off Priestley's work to find out how plants regenerate air and realized that plants need light to live and grow. Jean Senebier noticed that when exposed to sunlight, plants create oxygen out of carbon dioxide. Joseph Bienaimé Caventou and Pierre-Joseph Pelletier analyzed plant cells and discovered chlorophyl, a green pigment that transforms the air with the help of sunlight. In 1893, Charles Barnes described the biological process that uses energy from light to create chemical energy, which he called photosynthesis.