By 1800,hand printers could not supply enough books to satisfy [使满意] the demand.Books were not printed fast enough when hand-made paper and wooden hand presses were used.Fortunately [幸运地], about this time, many machines were invented that aided[辅助的] in the mass production of such products as cotton and woolen cloth.The invention of new types of printing machines and paper machines followed on the heels[后跟] of these inventions and helped to speed up the production of books.The paper machine produced paper in rolls instead of sheets; and the iron hand press enabled the printer to use larger pieces of paper on which more text could be printed in less time.Question: About 1800, when machines were developed, ______________.