In 1798, Mathus published a book, called "An Essay on the Principle of Population". In it, he describes the Malthusian growth model. He wrote that the growth of the population is exponential. The growth of the food supply however is only arithmetical. This means if there are no limits to the growth of the population, that it will not be possible to produce food for all of them. This is known as Malthusian catastrophe. Malthus wrote during the time of the Manchester School of thought.