100 ~=Sir H. Davy on the Preservation of Copper, §c. 
with security, has, by the application of protectors of 1-70th, 
made this voyage *, without apparently any wear of her sheet- 
ing; and that she is now preparing with the same protectors 
to make another voyage. 
In cases when ships are to be newly sheathed, the experi- 
ments which have been detailed in the preceding pages render 
it likely, that the most advantageous way of applying protection 
will be under, and not over the copper: the electrical circuit 
being made in the sea water passing through the places of 
junction in the sheets; and in this way every sheet of copper 
may be provided with nails of iron or zinc, for protecting 
them to any extent required. By driving the nail into the 
wood through paper wetted with brine above the tarred paper, 
or felt, or any other substance that may be employed, the in- 
cipient action will be diminished; and there is this great ad- 
vantage, that a considerable part of the metal will, if the pro- 
tectors are placed in the centre of the sheet, be deposited and 
re-dissolved: so there is reason to believe that small masses 
of metal will act for a.great length of time. Zinc, in conse- 
quence of its forming little or no insoluble compound in brine 
or sea water, will be preferable to iron for this purpose; and 
whether this metal or iron be used, the waste will be much 
less than if the metal was exposed on the outside: and all dif- 
ficulties with respect to a proper situation in this last case are 
avoided. 
The copper used for sheathing should be the purest that 
can be obtained ; and in being applied to the ship, its surface 
should be preserved as smooth and equable as possible: and 
the nails used for fastening should likewise be of pure copper ; 
and a little difference in their thickness and shape will easily 
compensate for their want of hardness. 
In vessels employed for steam navigation the protecting 
metal can scarcely be in excess+, as the rapid motion of these 
ships prevent the chance of any adhesions; and the wear of 
ne copper by proper protection is diminished more than two- 
thirds. ; 
* The Dorothy. 
+ I have mentioned in the two last communications on this subject some 
application of the principle ; many others will occur. In submarine con- 
structions—to protect wocd, as in piles, from the action of worms, sheathing 
of copper defended by iron in excess may be used: when the calcareous 
matter deposited will gradually form a coating of the character and firm- 
ness of hard stone, 
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