334 
Sir Humphry Davy's further researches on 
of the oxygen dissolved in the water when its quantity 
is limited, by the oxidable metal, and of course the propor- 
tion of this metal must be much larger when the water is 
constantly changing ; but the experiments seem to show that 
any diminution of protecting effect at a distance, does not 
depend upon the nature of the metallic, but of the imperfect 
or fluid conductor. 
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 whatever lengths of wire of of an inch were 
used, there was no dimunition of the protecting effect of the 
zinc ; and the experiment was carried so far as to employ 
the whole of a quantity of extremely fine wire, amounting to 
upwards of forty feet in length, and of a diameter equal, only 
to of an inch, when the results were precisely the same 
as if the zinc and copper had been in immediate contact. 
Pieces of charcoal, which is the worst amongst the more 
perfect conductors, were connected by being tied together, and 
made the medium of communication between zinc and copper, 
upon the same principles, and with the same views as those 
just described, and with precisely the same consequences. 
In my first experiments upon the effects of increasing the 
length or diminishing the mass of the imperfect or fluid con- 
ducting surface in interfering with the preserving effects of 
metals, I used long narrow tubes ; but I found them very in- 
convenient ; and I had recourse to the more simple method 
4 ( 
of employing cotton or tow for this purpose. 
Several feet of copper wire in a spiral form were connected 
