In 1795, having resigned his position in the service of the state, because of his desire for travel and scientific work, with two friends, Freiesleben, and Lieutenant Reinhard von Haften, of Westphalia, he journeyed to Venice, going through the Tyrol and the Alps into Switzerland. They visited the mountains around Schaffhausen, Zürich, and Berne, and such notable men of science as De Luc, Pictet, and Saussure. As Freiesleben said, "No subject having any reference to the physical constitution of the earth, the atmosphere, or any point of natural history, was allowed to escape his attention." An especial bond united Humboldt and the highly educated Von Haften, since between the latter's sister Minette and the young scientist there existed a devoted affection. This was cherished for ten years, but Humboldt's life of travel and exposure prevented a union which both ardently desired. He sacrificed his affections to science, and the loneliness of his later years proved the unwisdom of his choice. On his return home, Humboldt set himself earnestly to the writing of two books: one on geology, the disposition of strata in mountain masses; the other on the "Excitability of the Nerves and Muscles," describing over four thousand experiments. His devotion to science was shown by the painful experiments upon his own body, which brought permanent harm to his nervous system. He wrote to a friend: "I applied two blisters to my back, each of the size of a crown-piece, and covering respectively the trapezius and deltoid muscles.... When the blisters were cut, and contact made with zinc and silver, I experienced a sharp pain, which was so severe that the trapezius muscle swelled considerably, and the quivering was communicated upwards to the base of the skull and the spinous processes of the vertebræ." He also experimented with the noxious gases in mines, inventing lamps which were the forerunner of Sir Humphrey Davy's. Sometimes he was deprived of consciousness by the gases and saved only by the timely aid of friends. Always longing for foreign travel, he went to Weimar, to make himself more fully ready for it, especially by the study of anatomy. Here lived his brother William, who had married a brilliant and intellectual woman, the intimate friend of the wife of Schiller.