The conventions of the Republic of Letters were a great convenience to scholars throughout Europe. Scholars in correspondence with each other felt free to ask for assistance in research whenever it was necessary; indeed one of the functions of the "commerce de lettres", the purely literary correspondence, was to promote opportunities for research. Even cities which could in no sense be called isolated, such as Paris or Amsterdam, always lacked certain amenities of scholarship. Many books published in the Netherlands, for example, only found their way to Dutch presses because they were prohibited in France. Manuscripts necessary for research were often in libraries inaccessible to people in other towns. Literary journals usually could not provide enough information with sufficient rapidity to satisfy the needs of most scholars.