92 Sir H. Davy’s further Researches 
sailing, and which on the most exposed part of the ship, and 
in the most rapid course, bears a relation to it of nearly 2 to 
4°55. 
I used the very delicate balance belonging to the Royal So- 
ciety in these experiments; the sheets of copper weighed be- 
tween 7 and 8000 grains; and I was fully enabled to ascertain 
by means of this balance a diminution of weight upon so large 
a quantity, equal to 1-100th of a grain. It was evident from 
a very minute inspection of the sheet with the largest quantity 
of protecting metal, that there was not any adhesion of alka- 
line or earthy substances to its surface. 
Having observed, in examining the results of some of the 
experiments on the effects of single masses of protecting metal 
on the sheeting of ships, that there was in some cases in which 
sheets with old fastening had been used, tarnish or corrosion, 
which seemed to increase with the distance from the protecting 
metal, it became necessary to investigate this circumstance, 
“and to ascertain the extent of the diminution of electrical ac- 
tion in instances of imperfect or irregular conducting surfaces. 
With single sheets or wires of copper, and in small confined 
quantities of sea water, there seemed to be no indications of 
diminution 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 1-4000th part of the whole sur- 
face; and a copper wire of several feet in length was prevented 
from tarnishing by a piece of zine wire which was less than 
1-1400th 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 pro- 
tecting influence upon the same minute scale was exhibited 
for many days. A part of these results depend upon the ab- 
sorption 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 much larger when the water is constantly 
changing; but the experiments seem to show that any diminu- 
tion of protecting effect at a distance does not depend upon 
the nature of the metallic, but of the imperfect or fluid con- 
ductor. } 
This indeed is shown by many other results. 
A piece of zinc and a piece of copper in the same vessel of 
sea water, but not in contact, were connected by different 
lengths of fine silver wire of different thickness. It was found 
that 
