Transactions of the Royal Society. 345 



boat, to make these researches. Sheets of copper, carefully weighed, 

 and with different quantities of protecting metal, and some unpro- 

 tected, were exposed upon canvas, so as to be electrically insulated 

 upon the bow of the steam-boat, and were weighed and examined 

 at different periods, after being exposed in the north seas to the 

 action of the water during the most rapid motion of the vessel. 

 Very rough weather interfered with some of these experiments, and 

 many of the sheets were lost, and the protectors of others were 

 washed away ; but the general results were as satisfactory as if 

 the whole series of the arrangements had been complete. It was 

 found that undefended sheets of copper of a foot square lost about 

 6.55 grains in passing at a rate averaging that of eight miles an 

 hour in twelve hours ; but a sheet, having the same surface, de- 

 fended by rather less than 3-^y, lost 5.5 grains ; and that like sheets 

 defended by -fo and T ^ of malleable iron were similarly worn, 

 and underwent nearly the same loss, that of two grains, in passing 

 through the same space of water. These experiments (the results 

 of which were confirmed by those of others made during the whole 

 of a voyage to and from Heligoland, but in which during the 

 return the protectors were lost) show that motion does not affect 

 the nature of the limits and quantity of the protecting metal ; and 

 likewise prove, that independently of the chemical, there is a me- 

 chanical wear of the copper in sailing, and which, on the most ex- 

 posed part of the ship, and in the most rapid course, bears a 

 relation to it of nearly 2 to 4.55." 



The author next proceeds to detail a series of experiments 

 having for their object " to ascertain the extent of the diminution 

 of electrical action in instances of imperfect or irregular conduct- 

 ing surfaces." 



With single sheets or wires of copper, and in small confined 

 quantities of sea-water, there seemed to be no indications of dimi- 

 nution of conducting power, or of the preservative effects of zinc 

 or iron, however divided or diffused the surface of the copper, 

 provided there was a perfect metallic connexion through the mass. 

 Thus, a small piece of copper containing about 32 square inches, 

 was perfectly protected by a quantity of zinc which was less than 

 itjVtt P art °f tne whole surface ; and a copper wire of several feet 

 in length was prevented from tarnishing by a piece of zinc-wire 

 which was less than -j^ 1 ^ part of its length. In these cases the 

 protecting metal corroded with great rapidity, and in a few hours 

 was entirely destroyed ; but when applied in the form of wire and 

 covered, except at its transverse surface, with cement, its protect- 

 ing influence upon the same minute scale was exhibited for many 

 days. A part of these results depend upon the absorption of the 

 oxygen dissolved in the water when its quantity is limited, by the 

 oxidable metal, and of course the proportion of this metal must be 



