The Electric "Circuit" - 1748
William Watson (1715 - 1787)

An early treatise on electricity by one of its earliest proponents, Sir William Watson, a leading figure in the Royal Society and described as one of "the most distinguished name in this period of the history of electricity"³

It is to him we owe the term circuit. Watson was the first to observe the flash of light from the discharge of a Leyden jar, as well as providing the first demonstration of the passage of electricity through a vacuum, and the plus and minus of electricity.

Watson wrote almost all his works for the Philosophical Transactions of the Royal Society, but due to the demands of an eager and wider audience, many were published in pamphlet form in advance of the periodical's publication. The present work is notable for containing 'Le Monnier's experiment in a pond near the Tuilleries, p. 3; Watson's experiment on the Thames, p. 5; the coatings of the Leyden jar used on this noteworthy occasion were iron filings and sheet lead, p. 5; one-mile circuit, p. 40; velocity of sound and electricity pp. 42. 47; flashes inside jar at time of discharge p. 74'⁴

His experiments to determine the velocity of electricity are of particular interest. The general belief at that time was that electricity was faster than sound, but no accurate test had as yet been devised to measure the velocity of a current. Watson, in fields north of London, laid out a line of wire supported by dry sticks and silk which ran for 12,276 feet. Even at this length the 'Velocity of Electricity was instantaneous.' (p. 54). Resistance in the wire was also noticed but apparently not fully understood, as Watson relates that 'we observed again, that although the electrical compositions were very severe to those who held the wires, the report of the Explosion at the prime Conductor was little, in comparison of that which is heard when the Circuit is short.' (ibid). Watson eventually decided not to pursue his electrical experiments concentrating instead upon his medical career, but he continued to support others in presenting evidence to the Royal Society and became a champion of Benjamin Franklin.

This copy was previously owned by Herbert McLean Evans, the discoverer of Vitamin E, and William A. Cole, the distinguished collector and bibliographer of chemistry.