corrosion of copper sheeting hy sea water, &c. 157 
copper, containing about forty square inches, and the whole 
plunged below the surface of sea water ; it was found, after 
a week, that the copper was defended by the iron in the same 
manner as if it had been in immediate contact. 
A piece of copper and a piece of zinc soldered together at 
one of their extremities, were made to form an arc in two 
different vessels of sea water ; and the two portions of water 
were connected together by a small mass of tow moistened 
in the same water : the effect of the preservation of the 
copper took place in the same manner as if they had been 
in the same vessel. 
As the ocean may be considered, in its relation to the quan- 
tity of copper in a ship, as an infinitely extended conductor, 
I endeavoured to ascertain whether this circumstance would 
influence the results ; by placing two very fine copper wires, 
one undefended, the other defended by a particle of zinc, in 
a very large vessel of sea water, which water might be con- 
sidered to bear the same relation to so minute a portion of 
metal as the sea to the metallic sheeting of a ship. The re- 
sult of this experiment was the same as that of all the others ; 
the defended copper underwent no change ; the undefended 
tarnished, and deposited a green powder. 
Small pieces of zinc were soldered to different parts of a 
large plate of copper, and the whole plunged in sea water : 
it was found that the copper was preserved in the same 
manner as if a single piece had been used. 
A small piece of zinc was fastened to the top of a plate of 
polished copper, and a piece of iron of a much larger size 
was soldered to the bottom, and the combination placed in 
sea water. Not only was the copper preserved on both sides 
