In a letter to a colleague, Isaac Newton wrote, "If I have seen farther, it is by standing on the shoulders of giants." Which earlier work made Newton's scientific contributions possible or is most closely related to Newton's work? The research on population growth by Thomas Malthus The theory of planetary motion developed by Nicolaus Copernicus The use of the microscope to study cells by Robert Hooke The process for making stronger steel invented by Henry Bessemer