> Thank you for your answer. Is there anybody who has other literature??? > > Klaus Eichholz
Readers may want to look into my article "Foster's Diametral Sundial" which appeared in the Bulletin of the British Sundial Society (92-1, Feb. 1992) and subsequently in the North American Sundial Society's journal Compendium (3-2,June 1996). The initial two paragraphs of that article are as follows: "The diametral sundial, described in the work of Samuel Foster, a professor of astronomy at Gresham College in seventeenth century London, is a horizontal dial with movable stile. Its hour-points all lie on a finite segment of a straight line so that the shadow becomes retrograde daily at a selected hour. The intersection of the stile's shadow with the timeline marks the time of day. It progresses along the straight line until the appointed hour each day, at which time it slows to a halt and reverses direction, retracing its path." "Thus, Foster provides a simple means of recreating the Biblical miracle of Ahaz' dial, whose shadow behaves in much the same way. Note, however, that it is unlikely that Foster had this result as a goal for his research. The diametral dial is simply a special form of the more general elliptical dials he developed, including the earliest English derivation of the analemmatic dial and the original discovery of the circular hour-arc dial often attributed today to J.H. Lambert (1775)." Fred Sawyer
