The published works were unquestionably responsible for much of the training in the making of mathematical instruments in America, although no documentary evidence has yet been recovered to prove it. Another important influence on early American instrument-making which must be noted was that of the clockmaker as an artisan. A comprehensive study of surviving instruments and related records has revealed that only a few of the many clockmakers working in the American Colonies in the 18th century made mathematical instruments. Yet, a large proportion of the surviving surveying and nautical instruments produced before 1800 were the work of clockmakers. Classic among these must be noted the instruments produced by the brothers David and Benjamin Rittenhouse (see p. 15 and figs. 3 and 4), as well as the fine surveying instruments made by four separate members of the Chandlee family, whose clockmaking traditions began early in the 17th century (see p. 54). [Illustration: Figure 3.--Transit telescope made by David Rittenhouse and used by him for the observation of the transit of Venus in 1769. Brass, 33-1/2-in. tube on a 25-in. axis, with an aperture of 1-3/4 in. and a focal length of 32 in. Photo courtesy the American Philosophical Society.] [Illustration: Figure 4.--Surveying compass marked "Potts and Rittenhouse." Believed to be the work of David Rittenhouse in partnership with Thomas Potts. Photo courtesy the American Philosophical Society.] Finally, one must not overlook the fact that examples of English and other European instruments were available in the Colonies, and that at least some of the early colonial makers undoubtedly copied them. It is apparent from some surviving early American instruments that the materials, designs, dimensions, and details of European prototypes had been deliberately copied. It is possible to see in public collections, for instance, a Davis quadrant of English manufacture exhibited beside a later example, signed by a New England maker, which comes extraordinarily close to duplicating it in every feature. As with the presumed influence of published works, the practice of copying imported instruments cannot be documented, but it must have been engaged in by many of the unschooled New England instrument makers. By this means some may even have profited to the degree that they became professional craftsmen without benefit of formal apprenticeship.