ABSTRACT
At the end of his time in Geneva in the spring of 1677, Jacob , who was then 23 years old, received word of a position in France tutoring the children of the Marquis de Lostanges . e marquis off ered to pay for his journey by carriage to Nède near Limousin in south-central Franc e, where once again he would serve as a tutor. Since Jacob had determined that he needed to journey to France to continue his study of mathematics , he was pleased to take advantage of this off er. Once again he found time to explore mathematics during some free afternoons. At this time, Jacob made a serious study of sundial s and their construction, perfecting a method for determining the angle for the gnomon (the rod that creates the shadow from which the time is read) to accommodate the latitude of a specifi c location based on the tilt of the earth at that point. e angle is critical if the sundial is to be usable during daylight hours throughout the year. A properly constructed sundial’s only limitation is the need for clear sunny weather and a southern exposure.
