A particular hub for visionary inventors of all sorts was the Charles Williams machine shop on Court Street, where almost all of Bell's earliest telegraphic devices were constructed. The ­Williams shop, which built prototypes for many top inventors of the period, employed roughly two dozen machinists, including the young Thomas Watson, whom Bell eventually hired. In his autobiography, Watson described it as a "thrilling place" buzzing and clattering with the din of lathes and metalworking tools as workers turned out an array of strange new electrical devices, from telegraph relays to galvanometers. Even young Thomas Edison set up a lab above the shop so he could easily avail himself of its services. There, before Bell's arrival in Boston, Edison had won his very first patent, in 1869--for an electrical vote recorder.

In 1872, Bell started attending MIT's public lectures on experimental mechanics, including one in October by Professor Charles R. Cross that began a long, fruitful collaboration. At the talk, Cross demonstrated a device invented by his colleague Edward C. ­Pickering, who then chaired MIT's physics department. Pickering's so-called tin-box receiver had a thin metal diaphragm that vibrated when a current passing through an electromagnet was interrupted. As a result, it could crudely reproduce, on the other end of a telegraph line, the sound of a tuning fork rigged so that its vibrations would make and break a battery-­powered electrical circuit.

No one had yet conceived of how to translate the sound waves from the human voice into an electrical current, and Pickering's primitive receiver couldn't even have emitted them. (That part of the telephone puzzle--the design of the transmitter--makes up the mystery at the heart of my 2008 book, The Telephone Gambit.) Nonetheless, Pickering was one of the very first to develop a device that could pick up musical tones sent over telegraph wires. Bell was already keenly interested in this subject, and the exposure to Pickering's research surely spurred on his labors.

At the time of Cross's lecture, MIT (which had been incorporated in 1861 on the Boston side of the Charles River) had recently opened the Rogers Laboratory of Physics in a new building on Boylston Street. The facility was the first of its kind in the United States, a well-outfitted working laboratory that allowed students to conduct experiments illustrating the physical laws they learned about in class. Of particular interest to Bell, the new laboratory had an impressive set of equipment identical to that used in the pathbreaking work of Hermann von Helmholtz, one of the world's leading acoustical researchers.

In 1873, Bell accepted a position as a professor of vocal physi­ology and elocution at the fledgling Boston University (which had been chartered in 1869). The post drew him into even closer contact with Boston's scientific community, affording him the chance to get better acquainted with Professor Cross, who would eventually succeed Pickering as chair of MIT's physics department.