William Stackpole (1819–1895) and Robert Stackpole (1823–1873) were Irish immigrants who arrived in the United States in 1833. Trading as Stackpole & Brother, they began making mathematical instruments in 1851. During the Civil War, they made spyglasses and sextants for the Navy. Each Stackpole instrument is marked with a serial number, and the sale of instrument #655 in 1866 suggests that the firm averaged some 44 instruments per year. According to the 1870 Census of Industry, the Stackpoles had $12,000 invested in the firm, hired eleven men and two children, and were then producing 250 surveying and nautical instruments worth $26,900. In the early 1870s they made astronomical transit instruments for the American expeditions sent to observe the transit of Venus. The firm remained in business until 1910.