As no doubt now exists as to the principle of the protection of iron by zinc, the bolts and nails may be expected to remain free from rust as long as the more oxidable metal lasts; but with regard to the success of the iron sheathing, it is impossible to entertain the same confidence; for what, in this case, is to prevent the adhesion of shell-fish and sea-weed upon its surface? Let it be remembered, that it is only when the copper is in the act of solution in sea-water that the sheathing remains clean. In the year 1829, the Tender to the Flagship at Plymouth had her copper on one side of the bottom painted with white lead: in six months, this side was covered with long weeds; while the other side, which had been left bright, and consequently exposed to the solvent action of the salt-water, was found entirely free from all such adhesions. CHAPTER XIV. The failure of the Ship protectors a source of great vexation to Davy.--His Letters to Mr. Poole.--He becomes unwell.--He publishes his Discourses before the Royal Society.--Critical Remarks--and Quotations.--He goes abroad in search of health.--His Letter to Mr. Poole from Ravenna.--He resigns the Presidency of the Royal Society.--Mr. Gilbert elected _pro tempore_.--Davy returns to England, and visits his friend Mr. Poole.--Salmonia, or Days of Fly-fishing.--An Analysis of the Work, with various extracts to illustrate its character. The friends of Sir Humphry Davy saw with extreme regret that the failure of his plan for protecting copper sheathing had produced in his mind a degree of disappointment and chagrin wholly inconsistent with the merits of the question; that while he became insensible to the voice of praise, every nerve was jarred by the slightest note of disapprobation. I apprehend, however, that the change of character which many ascribed to the mortification of wounded pride, ought in some measure to be referred to a declining state of bodily power, which had brought with it its usual infirmities of petulance and despondency. The letters I shall here introduce may perhaps be considered as indicating that instinctive desire for quiet and retirement which frequently marks a declining state of health, and they will be followed by others of a less equivocal character. TO THOMAS POOLE, ESQ. Grosvenor Street, Nov. 24, 1824. MY DEAR POOLE, It is very long since I have heard from you, Mr. A----, whom you introduced to me, has sometimes given me news of you, and I have always heard of your health and well-being with pleasure. My immediate motive for writing to you now is somewhat, though not entirely selfish. You know 1 have always admired your neighbourhood, and I have lately seen a place advertised there, called, I think,----, not far from Quantock, and combining, as far as advertisement can be trusted, scenery, fishing, shooting, interest for money, &c.