Measuring the Height of a Tower with a Jacob's Staff

The image shows two men in 17th-century European civilian dress—wearing brimmed hats, doublets, and breeches—standing at two distinct distances from a vertical tower. The man on the left (labeled 'a') and the man on the right (labeled 'b') hold a Jacob's staff, a surveying tool consisting of a cross-piece sliding along a graduated rod, which they position before their eyes. Dotted lines extend from their instruments to the top ('D') and bottom ('C') of the tower, illustrating the principles of triangulation and geometric measurement. The background is printed over faint, mirrored text, indicating this page was taken from a printed scientific treatise.

This illustration reflects the early modern emphasis on practical geometry and the application of mathematical instrumentation to land surveying and architectural documentation. It exemplifies the period's pursuit of standardized measurement methods essential to the advancement of natural philosophy and the physical sciences.