Surveyor's Vernier Compass
"W.L. POTTS Bucks Penna."
length 14.25 inches; needle 5 inches
William Lukens Potts (1771-1854) worked with Benjamin Rittenhouse in the years 1796-1798, making plain and vernier compasses. In 1800, now in business on his own, he advertised "surveying instruments of all kinds, and Rittenhouse' Circumferentors, with each a nounes and spirit level compleat." This compass was made between 1807, when Potts bought land in Bucks County, Pennsylvania, and 1817, when he moved to Philadelphia. It has a variation arc on the south arm that extends 15 degrees either way; the "folded" vernier is moved by rack and pinion, and reads to 5 minutes. There is a spirit level on the north arm. A copy of Thomas Whitney's 1814 discussion of "The Variation of the Compass" is pasted into the inside cover of the wooden box holding this compass.