Lunar Society. In 1758 the Pennsylvania printer Benjamin Franklin, the leading experimenter in electricity, journeyed to Birmingham during one of his lengthy stays in Britain; Boulton met him, and introduced him to his friends. Boulton worked with Franklin in efforts to contain electricity within a Leyden jar, and when the printer needed new glass for his "glassychord" (a mechanised version of musical glasses) he obtained it from Boulton. Despite time constraints imposed on him by the expansion of his business, Boulton continued his "philosophical" work (as scientific experimentation was then called). He wrote in his notebooks observations on the freezing and boiling point of mercury, on people's pulse rates at different ages, on the movements of the planets, and on how to make sealing wax and disappearing ink. However, Erasmus Darwin, another fellow enthusiast who became a member of the Lunar Society, wrote to him in 1763, "As you are now become a sober plodding Man of Business, I scarcely dare trouble you to do me a favour in the ... philosophical way." The Birmingham enthusiasts, including Boulton, Whitehurst, Keir, Darwin, Watt (after his move to Birmingham), potter Josiah Wedgwood and clergyman and chemist Joseph Priestley began to meet informally in the late 1750s. This evolved into a monthly meeting near the full moon, providing light to journey home afterwards, a pattern common for clubs in Britain at the time. The group eventually dubbed itself the "Lunar Society", and following the death of member Dr William Small in 1775, who had informally co-ordinated communication between the members, Boulton took steps to put the Society on a formal footing. They met on Sundays, beginning with dinner at 2 pm, and continuing with discussions until at least 8. While not a formal member of the Lunar Society, Sir Joseph Banks was active in it. In 1768 Banks sailed with Captain James Cook to the South Pacific, and took with him green glass earrings made at Soho to give to the natives. In 1776 Captain Cook ordered an instrument from Boulton, most likely for use in navigation. Boulton generally preferred not to take on lengthy projects, and he warned Cook that its completion might take years. In June 1776 Cook left on the voyage on which he was killed almost three years later, and Boulton's records show no further mention of the instrument. In addition to the scientific discussions and experiments conducted by