Having served for a number of years as an officer in our Indian army, Mr. Cooke came back to Europe to recruit his health in the beginning of 1836, and took up his abode at Heidelberg. He found agreeable occupation for his leisure in the study of anatomy, and in the construction of anatomical models for his father's museum at Durham, where he was a professor in the university. Entirely self-taught in this delicate art, Mr. Cooke applied himself to it with characteristic ardour, and attained remarkable skill. One day he happened to witness some experiments which were made by Professor Moencke, to illustrate the feasibility of electric signalling. A current of electricity was passed through a long wire, and set a magnetic needle at the end quivering under its influence. The experiment was a very simple one, and not at all novel; but Cooke had never paid any attention to the subject before, and was much struck with what he saw. He became strongly impressed with the possibility of employing electricity in the transmission of telegraphic intelligence between distant places. From the day he witnessed the experiments in Professor Moencke's classroom, he forsook the dissecting knife, threw aside his modelling tools, and applied himself to the realization of his conception. With such ardour and devotion did he labour, and such skill and ingenuity did he bring to the work, that within three weeks he had constructed a telegraph with six wires, forming three complete metallic currents, and influencing three needles, by the varied inclination of which twenty-six different signals were designated. In that short time he had also invented the detector, by which injuries to the wires, whether from water, fracture, or contact with substances capable of diverting the current, were readily traced, and the alarum, by which notice is given at one end of the wire that a message is coming from the other. Both these contrivances were of the utmost value,--indeed, without them electric telegraphy would be impracticable,--and are still in use. Possessing more of a mechanical than a scientific genius, Mr. Cooke bestowed more of his time and ingenuity on the perfection of a telegraph to be worked by clock mechanism, set in action by the withdrawal of a detent by an electro magnet than in the completion of the electric telegraph pure and simple.