340 Sir Humphry Davy*s further researches on 
great rapidity, and the iron remains in the electro-negative 
and indestructible state. 
I began this paper by some observations upon the nature 
of the processes by which copper sheeting is destroyed by 
sea water, and on the causes by which it is preserved clean, 
or rendered foul by adhesions of marine vegetables or 
animals ; I shall conclude it by some further remarks on 
the same subject, and with some practical inferences and 
some theoretical elucidations, which naturally arise from the 
results detailed in the foregoing pages. 
The very first experiment that I made on harbour-boats 
at Portsmouth, proved that a single mass of iron protected 
fully and entirely many sheets of copper, whether in waves, 
tides, or currents, so as to make them negatively electrical, 
and in such a degree as to occasion the deposition of earthy 
matter upon them ; but observations on the effects of the 
single contact of iron upon a number of sheets of < copper, 
where the junctions and nails were covered with rust, and 
that had been in a ship for some years, showed that the 
action was weakened in the case of imperfect connexions by 
distance, and that the sheets near the protector were more 
defended than those remote from it. Upon this idea I pro- 
posed, that when ships, of which the copper sheathing was 
old and worn, were to be protected, a greater proportion of 
iron should be used, and that if possible it should be more 
distributed. The first experiment of this kind was tried on 
the Sammarang, of 28 guns, in March, 1824, and which had 
been coppered three years before in India. Cast iron, equal 
in surface to about of that of the copper was applied in 
four masses, two near the stern, two on the bows. She 
