158 Sir Humphry Davy on the corrosion , &c. 
in the same manner as in the other experiments, but even the 
iron ; and after a fortnight, both the polish of the copper and 
the iron remained unimpaired. 
7- I am continuing these researches, and I shall communi- 
cate such of them as are connected with new facts, to the 
Royal Society. 
The Lords Commissioners of the Admiralty, with their 
usual zeal for promoting the interests of the Navy by the 
application of science, have given me permission to ascertain 
the practical value of these results by experiments upon ships 
of war ; and there seems every reason to expect ( unless 
causes should interfere of which our present knowledge 
gives no indications ) that small quantities of zinc, or which 
is much cheaper, of malleable or cast iron, placed in contact 
with the copper sheeting of ships, which is all in electrical 
connection, will entirely prevent its corrosion. And as ne- 
gative electricity cannot be supposed favourable to animal 
or vegetable life ; and as it occasions the deposition of mag- 
nesia, a substance exceedingly noxious to land vegetables, 
upon the copper surface ; and as it must assist in preserving 
its polish, there is considerable ground for hoping that the 
same application will keep the bottoms of ships clean, a cir- 
cumstance of great importance both in trade and naval war. 
It will be unnecessary for me to dwell upon the economical 
results of this discovery, should it be successful in actual 
practice, or to point out its uses in this great maritime and 
commercial country. 
I might describe other applications of the principle to the 
preservation of iron, steel, tin, brass, and various useful 
metals ; but I shall reserve this part of the subject for 
another communication to the Royal Society. 
