Posthuma Fosteri: The Description Of A Ruler

by Samuel Foster

This book was published posthumously in the year that Foster died. It describes a ruler with 9 scales and gives instructions on how to use the scales to solve many of the standard problems of Òastronomie, navigation, and diallingÓ. In addition to familiar trigonometric scales, the ruler includes two new scales introduced by Foster. The first provides an easy means of laying out horizontal sundials between 30¼ and 60¼ of latitude without having to draw any auxiliary lines. The second is a true Foster with this scale and a chord scale, Foster is able to find all the elements needed to draw a sundial on an arbitrary plane. He also uses these scales to replace the usual dialing scales (also a Foster invention), laying out a sundial from equispaced points on the circumference of a circle. One page of the current edition includes a redrawn version of the ruler that the reader can use in conjunction with the text.

92 pages, Paperback

Published February 15, 2007