Some portraits include precisely delineated instruments, diagrams, and maps. By the 1740s, the possession of apparatus of science particularly such optical instruments as microscopes and telescopes, and such philosophical instruments as orreries, air pumps, and electrical machines was a marker of polite gentility in England. For serious investigators of nature, however, such instruments were essential for their work. And yet they were expensive, and in America they had to be imported, for the center of the scientific instrument trade was in London. Therefore, when an artist included a carefully drawn instrument in a portrait, it was probably one of the sitter's most valued possessions, and the most important marker of his scientific interests. John Singleton Copley's circa 1773 portrait of Harvard professor John Winthrop celebrates Winthrop's astronomical observations of the 1761 and 1769 transits of Venus, and includes a precise diagram of his observations, as well as his own gleaming brass telescope, made in London by James Short around 1758. Winthrop's telescope was given to Harvard after his death in 1779, and remains in the university collection. Winthrop was a well-known man of science who received honorary degrees from the University of Edinburgh and from Harvard. Others are all but forgotten today, such as John Vinall, a writing master and mathematics teacher in Boston, and David Wiley, a Presbyterian clergyman who moved to Georgetown (District of Columbia) around 1800 to run the Columbian Academy there. Wiley gave scientific lectures and demonstrations, and made use of an electrical machine, probably the one pictured in his portrait by Charles Peale Polk.