As small spring-driven shelf clocks became popular, Birge & Fuller of Bristol, Connecticut, introduced c. 1844 an eight-day movement powered by Joseph Ives's patented 'accelerating lever spring' (wagon spring), housed in a modified sharp-Gothic-on-frame case. This style is often referred to as 'steeple-on-steeple' or 'double-decker steeple'. There are two distinct styles, each produced in two sizes. The earlier, offered only by the Birge firm, had long candle-style finials on each side of the case, mounted on top of the lower frame. The large case for eight-day movements had double finials, and the smaller 30-hour movement case had single finials. The other style had the conventional finials found on the regular sharp Gothic case, with two mounted each side on top of the lower frame and two on top of the upper frame.