The library was also home to a host of international scholars. The library filled its stacks with new works in mathematics, astronomy, physics, natural history and other subjects. It was at the Library of Alexandria that the scientific method was first conceived and put into practice, and its empirical standards applied in serious textual criticism. As the same text often existed in several different versions, comparative textual criticism was crucial for ensuring their accuracy. Once ascertained, copies would then be made for scholars, royalty and wealthy bibliophiles the world over, this commerce bringing income to the library. The editors at the Library of Alexandria are especially well known for their work on Homeric texts. The more famous editors generally also held the title of head librarian. These included, among others,