At the end of five months, while only sixteen years of age, he forsook the trains, and accepted an offer of twenty-five dollars a month, with extra pay for overtime, as operator in the telegraph office at Port Huron, a small installation in a jewelry store. He worked hard to acquire more skill; and after six months, finding his extra pay withheld, he obtained an engagement as night operator at Stratford, in Canada. To keep him awake the operator was required to report the word 'six,' an office call, every half-hour to the manager of the circuit. Edison fulfilled the regulation by inventing a simple device which transmitted the required signals. It consisted of a wheel with the characters cut on the rim, and connected with the circuit in such a way that the night watchman, by turning the wheel, could transmit the signals while Edison slept or studied. His employment at Stratford came to a grievous end. One night he received a service message ordering a certain train to stop, and before showing it to the conductor he, perhaps for greater certainty, repeated it back again. When he rushed out of the office to deliver it the train was gone, and a collision seemed inevitable; but, fortunately, the opposing trains met on a straight portion of the track, and the accident was avoided. The superintendent of the railway threatened to prosecute Edison, who was thoroughly frightened, and returned home without his baggage. During this vacation at Port Huron his ingenuity showed itself in a more creditable guise. An 'ice-jam' occurred on the St. Clair, and broke the telegraph cable between Port Huron and Sarnia, on the opposite shore. Communication was therefore interrupted until Edison mounted a locomotive and sounded the whistle in short and long calls according to the well-known 'Morse,' or telegraphic code. After a time the reporter at Sarnia caught the idea, and messages were exchanged by the new system. His next situation was at Adrian, in Michigan, where he fitted up a small shop, and employed his spare time in repairing telegraph apparatus and making crude experiments. One day he violated the rules of the office by monopolising the use of the line on the strength of having a message from the superintendent, and was discharged.