829 
Protecting the Copper-Sheathing of Ships . 
course: Nor am I aware of any experiment or induction which 
would lead us to infer, if negative electricity be as hostile to such 
animals as has been rather hastily inferred, that the increase of 
this electric current should be favourable to their accumulation 
on the copper. 
The fact, that, when two metals of different degrees of oxida- 
bility are in contact, in a saline liquid, the least oxidable will es- 
cape corrosion, has long been familiar to chemists ; but this does 
not diminish the merit of the distinguished individual, who first 
applied this fact to the important purposes of preserving the 
copper of ships. That this plan will not always prevent the ad- 
hesion of parasitical animals, the experiments made at this port 
have decided ; but, notwithstanding the decided and unfavour- 
able opinion of our practical men, it does not yet appear to me 
certain, that the ships were considerably more foul than if there 
had been no defence ; and, at any rate, the copper has, in every 
instance, been saved. Many more experiments must be made, 
before we can ascertain which mode is most liable to foulness ; 
and, in the mean time, it is of importance that every fact, on 
either side of the question, be candidly laid before the public. 
The point is not to be solved by hypothetical explanations, but 
by a careful collection and comparison of facts. 
In the instances before us, how far the uncommon foulness of 
the bottoms of the Tickler and the Dorothy was owing to the 
mode of defence, it is difficult to determine : for the copper of 
the ships Dee and Huskisson appears to have been clean ; al- 
though they had performed voyages well known to be equally 
favourable to the adhesion of barnacles. 
The ship Huskisson , belonging to Mr Horsfall, was lately 
in dock, after a voyage to and from Demerara, where she lay 
some weeks, in a river remarkably favourable to the adhesion of 
parasitical animals and weeds ; yet, when I examined this vessel, 
her copper appeared perfectly clean, as far as could be seen, 
when she w^as purposely set by the stern in unloading, in order 
to shew her copper at the bows as low as possible. The cap- 
tain stated, that, before coming into port, while yet in clear 
water, he had seen her bottom, even to the keel, and it seemed 
to him quite clean. This ship was defended by a bar of malle- 
