In December, 1821, Davy paid a visit to his old home in Penzance, and saw his mother for the last time before her death. A public dinner was given him by his townsmen, which honor he greatly appreciated. He was no longer the poor lad among them. "Every heart, tongue, and eye were as one to do honor to him who had not only rendered the name of their _town_ famous and imperishable as science itself, but who had added lustre to the intellectual character of their _country_." From year to year he continued his experiments. Urged by the commissioners of the navy to remedy the corrosion of copper sheathing on vessels by sea water, he succeeded in rendering the copper negatively electrical by small pieces of tin, zinc, or iron nails. Shells and seaweeds adhered to the non-corroded surface, but the principle of galvanic protection has been applied to various important uses. In 1824, Sir Humphrey took a journey to Norway, Sweden, and Denmark, visiting Berzelius of Sweden, "one of the great ornaments of the age," he said, and Oersted of Denmark, distinguished for his discovery of electro-magnetism. Towards the close of 1826, when he was only forty-eight, Davy was attacked by paralysis in the right side, having suffered for a year with numbness and pain in his right arm. During his confinement in his room, he corrected the proof sheets of his "Discourses to the Royal Society," published in January, 1827. In this year, having improved, he went through France, Italy, and Switzerland, hunting and fishing as in his boyhood, and writing "Salmonia, or Days of Fly Fishing," giving descriptions of his journey and his observations on natural history. In the spring of 1828, he made another journey, to Southern Austria, spending the winter in Italy, and writing his "Consolation in Travel," which Cuvier called the work of a dying Plato. "I was desirous," he says, "of again passing some time in these scenes, in the hope of reëstablishing a broken constitution; and though this hope was a feeble one, yet, at least, I expected to spend a few of the last days of life more tranquilly and more agreeably than in the metropolis of my own country. Nature never deceives us. The rocks, the mountains, the streams, always speak the same language. A shower of snow may hide the verdant woods in spring; a thunder storm may render the blue limpid streams foul and turbulent: but these effects are rare and transient; in a few hours, or at least days, all the sources of beauty are renovated; and Nature affords no continued trains of misfortunes and miseries, such as depend upon the constitution of humanity,--no hopes forever blighted in the bud,--no beings full of life, beauty, and promise, taken from us in the prime of youth. Her fruits are all balmy, bright, and sweet; she affords none of those blighted ones so common in the life of man, and so like the fabled apples of the Dead Sea,--fresh and beautiful to the sight, but, when tasted, full of bitterness and ashes."