At this point, and before Bell had begun to experiment with his telegraph, the scene of the story shifts from Canada to Massachusetts. It appears that his father, while lecturing in Boston, had mentioned Graham's exploits with a class of deaf-mutes; and soon afterward the Boston Board of Education wrote to Graham, offering him five hundred dollars if he would come to Boston and introduce his system of teaching in a school for deaf-mutes that had been opened recently. The young man joyfully agreed, and on the first of April, 1871, crossed the line and became for the remainder of his life an American. For the next two years his telegraphic work was laid aside, if not forgotten. His success as a teacher of deaf-mutes was sudden and overwhelming. It was the educational sensation of 1871. It won him a professorship in Boston University; and brought so many pupils around him that he ventured to open an ambitious "School of Vocal Physiology," which became at once a profitable enterprise. For a time there seemed to be little hope of his escaping from the burden of this success and becoming an inventor, when, by a most happy coincidence, two of his pupils brought to him exactly the sort of stimulation and practical help that he needed and had not up to this time received. One of these pupils was a little deaf-mute tot, five years of age, named Georgie Sanders. Bell had agreed to give him a series of private lessons for $350 a year; and as the child lived with his grandmother in the city of Salem, sixteen miles from Boston, it was agreed that Bell should make his home with the Sanders family. Here he not only found the keenest interest and sympathy in his air-castles of invention, but also was given permission to use the cellar of the house as his workshop. For the next three years this cellar was his favorite retreat. He littered it with tuning-forks, magnets, batteries, coils of wire, tin trumpets, and cigar-boxes. No one outside of the Sanders family was allowed to enter it, as Bell was nervously afraid of having his ideas stolen. He would even go to five or six stores to buy his supplies, for fear that his intentions should be discovered. Almost with the secrecy of a conspirator, he worked alone in this cellar, usually at night, and quite oblivious of the fact that sleep was a necessity to him and to the Sanders family. "Often in the middle of the night Bell would wake me up," said Thomas Sanders, the father of Georgie. "His black eyes would be blazing with excitement. Leaving me to go down to the cellar, he would rush wildly to the barn and begin to send me signals along his experimental wires. If I noticed any improvement in his machine, he would be delighted. He would leap and whirl around in one of his `war-dances' and then go contentedly to bed. But if the experiment was a failure, he would go back to his workbench and try some different plan."