From 1823 to 1826 may be described as the last period of his scientific labours; and it was in a great measure devoted to investigations, undertaken at the request of the Government, into the best mode of preventing the destruction of the copper-sheathing of vessels by the action of the sea. This Davy to some extent accomplished by coating the copper with tin; but, unfortunately, the tin did not prevent (as the copper did) the fouling of the metal by accretions of seaweeds and shells; and the practical result was nil. He was much disappointed at this, having taken great pains in the matter, and having even made a voyage to the North Sea for the purpose of conducting his experiments. Of this excursion, which included visits to Norway, Sweden, and Denmark, he has left copious records--though, as a general rule, he had now discontinued his diary--and these include his reflexions not only on the scenery, etc., through which he passed, but, according to his custom, his impressions of the distinguished men of science and others with whom he came in contact. Those circumstances which impressed Davy most deeply he often recorded, as was his practice throughout his life, in verse. A specimen may be given here in the following fragment written at Ullswater, which he visited in August, 1825: 'Ye lovely hills that rise in majesty Amidst the ruddy light of setting suns, Your tops are bright with radiance, while below The wave is dark and gloomy, and the vale Hid in obscurest mist. Such is the life Of Man: this vale of earth and waters dark And gloomy--but the mountains range above! The sky--the heavens are bright!----' But he could not succeed in shaking off the illness of which he had had more than one warning; and even his elastic spirits began to flag under its depressing influence. The spring of 1826 found him worse; he complained much of rheumatism, and of slight numbness in his limbs; and the death of his mother in the autumn still further affected his health. With great pain and effort he delivered what proved to be his last address to the Royal Society--a body whose mission was so like his own, 'ad inquisitionem et inventionem naturæ veræ et interioris rerum omnium'--on St. Andrew's Day, 1826; and shortly after he suffered a slight attack of paralysis, which, however, did not prevent his revising his discourses, nor even deter him from projecting new scientific treatises. During his recovery he liked nothing better than having novels and romances read to him,--partly I should think to divert his mind from the small worries which were inevitable to one occupying the post which he filled, but which at this juncture pressed upon him with increasing force, and indeed probably conduced to his determining upon another visit to the Continent in January, 1827, accompanied on this occasion only by his brother, Dr. John Davy, an army surgeon.