In April 1874, after Bell addressed MIT students and faculty about his acoustical studies and his efforts to teach the deaf to speak, Cross--apparently impressed--granted him unfettered access to the Institute's facilities for his further research. Bell seized the opportunity. In May, he wrote to his parents about working at MIT with Cross in pursuit of an improved "phonautograph," a device creating a precise visual representation of different vocal sounds.

Over the next several years, Bell discussed a variety of scientific matters with Cross and sought his advice on numerous occasions. Some of the most detailed information about the work Bell did at MIT comes from depositions he and others made for lawsuits challenging his ownership of the telephone idea--lawsuits that continued for nearly two decades after he patented the device.

To hold onto his broad U.S. patent on the telephone, Bell downplayed the debt he owed to other inventors. In court, for instance, Bell claimed that he didn't remember much about the work of German inventor Philipp Reis, who by many accounts developed a working telephone as early as 1861, when Bell was still a teenager. But there is evidence to contradict Bell's claim. Not only did he cite Reis's work in his lecture to the American Academy, but Cross recalled under oath that he had personally spoken to Bell about Reis's telephone as early as the spring of 1874--nearly two years before Bell's telephone patent. In one of the incidents Cross recounted, a very excited Bell had come to him with an idea for what he believed was a new type of receiver, only to have Cross explain that Reis had already invented it. Although Cross never explicitly implicated Bell in wrongdoing, he testified that he had fully explained Reis's telephone device to Bell on two occasions.

Of course, Bell won his patent claim as the sole inventor of the telephone, and public knowledge about the contributions of others mostly faded into oblivion. The many surviving primary documents from the period, however, leave little doubt of the important supporting role that Cross and the Rogers Laboratory played in helping Bell gain vital, detailed, and often hands-on knowledge about the cutting-edge work of others in the field, including ­Pickering, Helmholtz, Reis, and Elisha Gray, the inventor whose pathbreaking design for a liquid transmitter Bell seems to have appropriated to make his world-famous call to Watson.

Many years later, with Bell's legal claim to the telephone long since secured, he publicly acknowledged Cross's contribution. Bell told the crowd of 1,500 assembled at Symphony Hall for MIT's 50th-anniversary gala--and more than 5,000 alumni and guests who were listening in by phone at Alumni Association gatherings across the country--that Cross had not only made "many advances in the telephone itself" but inspired many students to "go forth from the Institute to perfect the work."