In 1812 Davy was knighted by the Prince Regent. Only thirty-three, and he had come to great renown! And now an important change was to come into his life. During the preceding year he had become acquainted with Mrs. Appreece, towards whom esteem gradually ripened into affection. When their marriage had been decided upon, he wrote his mother: "I am the happiest of men, in the hope of a union with a woman equally distinguished for virtues, talents, and accomplishments.... You, I am sure, will sympathize in my happiness. I believe I should never have married but for this charming woman, whose views and whose tastes coincide with my own, and who is eminently qualified to promote my best efforts and objects in life." To his brother he writes: "I have been very miserable. The lady whom I love best of any human beings has been very ill. She is now well, and I am happy. Mrs. Appreece has consented to marry me: and when the event takes place I shall not envy kings, princes, or potentates.... I am going to be married to-morrow; and I have a fair prospect of happiness, with the most amiable and intellectual woman I have ever known." How love idealizes all things, makes a new heaven and a new earth for us! He found in her the two needed qualities for happiness; amiability, without which the life of a man is usually made wretched, and intellectuality, without which a cultivated man can have little companionship in a wife. The marriage seems to have been a happy one, for he writes to John later: "Lady D. is a noble creature, and every day adds to my contentment by the powers of her understanding, and her amiable and delightful tones of feeling." Like the wife of Herschel, she was a wealthy widow, so that after his marriage Davy was enabled to travel, and devote himself wholly to original investigation. He resigned his professorship at the Royal Institution after twelve most useful years. His "Elements of Chemical Philosophy" was now published, and dedicated to Lady Davy. After a pleasure trip with his wife to the highlands of Scotland, taking his portable chemical apparatus with him for study, they took a journey to France, Italy, Sicily, and Germany, accompanied by Mr. Michael Faraday, afterward so celebrated, then "his assistant in experiments and writing." In Paris, where he spent two months, he discovered that iodine is a simple substance, analogous to chlorine. Here he became the intimate friend of many distinguished men. "Humboldt," he said, "was one of the most agreeable men I have ever known; social, modest, full of intelligence, with facilities of every kind; almost _too fluent_ in conversation. His travels display his spirit of enterprise. His works are monuments of the variety of his knowledge and resources." Gay-Lussac he placed "at the head of the living chemists of France."