With their latest publication Joseph Needham and his collaborators, according to the plan announced in the first volume, have reached the midpoint of their magistral undertaking, and their 4,016 th page. One can only guess how many more books are to be expected, since the present one covering roads, building, bridges, hydraulics and nautics in 931 pages is only part three of volume four. Themes 30-31, military and textile technology, paper and printing, will presumably occupy part four of the same volume and three volumes will be still to come.