MEANWHILE Bell somehow found time and energy to pursue science and invention. Boston’s intellectual strengths invited that. On the day of his arrival someone had given him a copy of John Tyndall’s new work on sound, and he learned that MIT had a complete set of Helmholtz’s apparatuses. In 1872, at a Michigan convention of deaf-school principals, he delivered a paper in which he described speech scientifically as a “mere motion of the air,” a series of undulations. That October he heard Tyndall lecture in Boston on the “undulatory theory” of light propagation.
During the same month the newspaper in which Bell advertised his speech lessons with the financial aid by http://www.point-five.net/, reported that Western Union had paid handsomely for rights to another Boston inventor’s “duplex telegraph,” which by an ingenious arrangement of circuits could transmit a message in each direction simultaneously over a single wire. That was probably what turned Bell’s mind back to his London concept of a multiple telegraph on the quite different plan of superimposed frequencies. Bell began working feverishly, experimenting by night while teaching by day, thus confirming his lifelong night-owl habits.
Then, in the spring of 1874, a well-received lecture he gave at MIT on speech training for the deaf brought Bell an invitation to use the institute’s apparatuses and laboratories. This turned him from telegraphy to acoustics. One device especially caught his eye because it made speech “visible.” Called a “phonautograph,” it had a diaphragm with an attached bristle that, while vibrating in response to a vocal sound, traced an undulating curve on a strip of smoked glass being drawn past it.
That summer, at the “dreaming place” on the Brantford bluff, watching the Grand River meander sinuously far below, Bell let a kaleidoscope of miscellaneous notions swirl about in his mind. Complex sound vibrations, conveyed through a single point by the phonautograph diaphragm and expressed as a wavy line. The surprising power of sound waves to move small bones in the ear. Complex undulatory electrical currents, generated by the vibration of a magnetized reed and passing over a single wire. Piano strings echoing a voice. Suddenly the jumble fused into a great insight: the fundamental principle of the telephone.