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.
Here Humboldt and Goethe became earnest friends. Goethe says: "During Humboldt's visit, my time has been usefully and agreeably spent; his presence has had the effect of arousing from its winter sleep my taste for natural science." Years afterward Goethe said to Eckermann: "Alexander von Humboldt has been with me for some hours this morning; what an extraordinary man he is! Though I have known him for so long, I am always struck with fresh amazement in his company. He may be said to be without a rival in extent of information and acquaintance with existing sciences. He possesses, too, a versatility of genius which I have never seen equalled. Whatever may be the subject broached, he seems quite at home in it, and showers upon us treasures in profusion from his stores of knowledge. He resembles a living fountain, whence flow many streams, yielding to all comers a quickening and refreshing draught. He will remain here a few days, and I already feel that I shall have lived through years in the time."