As the increasing preoccupation with subdivision of land and with surveying led to a greater demand for suitable instruments, it was the skilled craftsmen of the community, such as the clockmaker and the silversmith, that were called upon to produce them. Superb examples also were produced by the advanced scientific men, or "mathematical practitioners," of the period. Colonial Training in Instrument Making One may well ask, where did these native craftsmen acquire the knowledge that enabled them to produce so skillfully the accurate and often delicate mathematical instruments? There were a number of possible sources for this knowledge. The first source lies in England, where some of these craftsmen could have studied or served apprenticeships. After completing their apprenticeship with English mathematical practitioners, they may have immigrated to the Colonies and taught the craft to others. This seems to be entirely plausible, and was probably true, for example, of Thomas Harland the clockmaker, Anthony Lamb, and perhaps several others. However, these were the exceptions instead of the rule, since a biographical study of the instrument makers in general reveals that they were for the most part native to America. It is not likely that the one or two isolated practitioners that had been trained in England could have taught so many others who worked in the same epoch. [Illustration: Figure 2.--Title page of _The Surveyor_ by Aaron Rathborne, published in London in 1616. The book was one of the sources of information for American makers of mathematical instruments.] Another source for this knowledge of instrument making was probably the reference works on the subject that had been published in England and in France. As an example, Nicolas Bion's _Traite de la Construction et des Principaux Usages des Instruments de Mathematique_, which had been first published in 1686, was translated into English by Edmund Stone in 1723, and went into several English editions. Copies of this work in English undoubtedly found their way to America soon after publication. Other popular works were Aaron Rathbone's _The Surveyor_, which appeared in London in 1616 (see fig. 2); William Leybourn's _The Compleat Surveyor_, in 1653; and George Atwell's _Faithfull Surveyour_, in 1662. Other works popular in the Colonies were R. Norwood's _Epitome, or The Doctrine of Triangles_ (London, 1659) and J. Love's _Geodasia, or the Art of Surveying_ (London, 1688). These works undoubtedly inspired similar publications in America, for many books on surveying and navigation appeared there before the beginning of the 19th century. Chief among them were S. Moore's _An Accurate System of Surveying_ (Litchfield, Conn., 1796), Z. Jess's _A Compendious System of Practical Surveying_ (Wilmington, 1799), Abel Flint's _Surveying_ (Hartford, 1804), and J. Day's _Principles of Navigation and Surveying_ (New Haven, 1817).