The best known member of the family was Walter Folger, Jr. (1765-1849), a self-taught clockmaker and watchmaker with great interest in the sciences. A telescope that he produced about 1818 was considered to be the finest in the country at that time. His greatest achievement was a tall case astronomical clock that he devised and constructed; it was completed in 1790 and is considered to be the most complicated domestic clock on record.[36] Folger also produced quadrants and compasses, and made astronomical observations. His observations of the solar eclipse of September 17, 1811, were published in 1815 in _Memoirs of the Academy of Arts and Sciences_. Probably one of the most significant of the surviving early American scientific instruments is a pair of gunners' calipers made and used by PAUL REVERE (1735-1818) of Boston. The calipers are made of incised brass, measuring 7 inches in length and 1-3/4 inches in width. They are signed on the reverse side with the name "Revere" in the style of script signature used by this maker in many of his engravings. The design of the instrument is substantially different from that which is commonly found in English, French, and German gunners' calipers of the period, and was probably Revere's own. (See figs. 19, 20.) [Illustration: Figure 18.--Orrery by Joseph Pope completed in 1787 for Harvard University. Engraved plates and bronze figures were made by Paul Revere. The orrery is 6-1/2 ft. in diameter and 6-1/2 ft. high. The twelve figures at the corners are said to have been carved in wood by Simeon Skillin and cast in bronze by Paul Revere. Photo courtesy Harvard University.] It is believed that these calipers, which are preserved in the collection of the Bostonian Society in Boston, were probably used by Revere in 1775-1776. This was the period during which he was in charge of ordnance repairs for the Continental Army, and involved in various ventures for the manufacture of gunpowder and the casting of cannon. There is no evidence of other scientific instruments made by Revere, lending some weight to the belief that these calipers were made for his own use. [Illustration: Figure 19.--Brass gunnery calipers made and probably used by Paul Revere (1735-1818). The calipers are 7 in. long and 1-3/4 in. wide.] [Illustration: Figure 20.--Reverse side of gunnery calipers, showing the inscribed signature. Photos courtesy the Bostonian Society, Boston, Mass.] Other Massachusetts instrument makers include Gideon Fairman (1774-1827) of Newburyport who was a partner of William Hooker in the firm of Hooker & Fairman, which dealt in mathematical instruments before 1810.[37] Fairman later moved to Philadelphia, where he was associated with the engraving firm of Draper, Murray & Fairman. At the end of the 18th century Samuel Emery was making mathematical instruments in Salem, at the same time that John Jayne was engaged in the same work in that community.[38]