Alfred Marshall (1842-1924) is considered as one of the most influential economists of his time. His specialty was microeconomics the study of individual markets and industries, as opposed to the study of the whole economy. His most important book was Principles of Economics (1890), which was for many years the Bible of British economics. Marshall was the first principal of University College, Bristol (1877-81), and a professor at the University of Cambridge (1885-1908), he reexamined and extended the ideas of classical economists such as Adam Smith and David Ricardo.