27*2 Proceeclmgs of the Royal Society. 



papers, the President proceeds, in the present communication, to 

 consider the circumstances under which various substances are 

 deposited upon the protecting copper, and their general influence 

 upon its wear, more especially in regard to ships in motion. 

 For this purpose, he availed himself of the use of a steam-boat, 

 employed on an expedition to ascertain some points of longi- 

 gitude in the north seas, and his inquiries lead to the inference 

 that motion does not affect the nature of the limits and quantity 

 of the protecting metal, and that independent of the chemical > 

 there is likewise a mechanical, wear of the copper, in sailing. 



In examining the results of some of the experiments upon the 

 effects of single masses of protecting metal on the sheathing, 

 the author observed, that in same cases, the corrosion seemed 

 to increase with the distance from the protecting metal. It 

 became, therefore, necessary to investigate this circumstance, 

 and to ascertain the extent of the diminution of electrical action, 

 in instances of imperfect or irregular conducting surfaces. Sir 

 Humphry detailed several curious and important experiments in 

 illustration of this inquiry, which prove that any diminution of 

 protecting effect, at a distance, does not depend upon the sur- 

 face of the metallic, but of the imperfect or fluid, conductor. 



His experiments upon perfect and imperfect conductors, led 

 Mm to another inquiry, important in its practical relations, re- 

 specting the nature of the contact between the copper and the 

 preserving metal. He found the protecting action prevented by 

 the thinnest stratum of air, or the finest leaf of talc, or dry 

 paper ; but the ordinary coating of rust, or a thin piece of 

 moistened paper, did not impair it. 



After some experimental details, respecting the electro-chemi- 

 cal powers of metals in solutions excluded from air. Sir Humphry 

 concluded his paper with practical inferences and theoretical 

 elucidations, arising out of its general details. Finding that in 

 certain cases of imperfect connexion, the influence of the 

 protector was weakened by distance, the author proposed that 

 when ships with old sheathing were to be protected, a greater 

 proportion of iron should be used, and, if possible, more distri- 



