328 
Dr Traill on Sir H. Davy’s Method of 
hour, it had become very hot, and smoked, and soon assumed 
the appearance of rusted particles of iron. The bars of iron 
had been very little reduced in substance during the voyage. 
“ With respect to the copper, such part of it as was not co- 
vered with barnacles appeared bright ; and, as far as I could 
judge from such an inspection of it, as perfect and entire as 
when it was put on ; but I never saw a ship's bottom more 
thickly studded with barnacles , nor any that were more difficult 
to scrape off. They were all rather small. It was only on the 
lower part of the bows, and about two inches above, and four 
inches below the iron-bars that the copper was not covered with 
barnacles ; excepting the upper part of it, which had been lit- 
tle under water. 
“ Several vessels are expected to return from the East and 
West Indies in the ensuing month, having had wrought- iron ap- 
plied in the same manner that the cast- iron was in the Tickler. 
(Signed) “ Charles Horsfall.” 
II. 
64 Dear Sir, Liverpool , May 19- 1825. 
“ In my communication of 17th March, I gave you the re- 
sult of one trial of Sir H. Davy’s method of defending the cop- 
per-sheathing of ships, by means of bars of iron. In that in- 
stance, the copper was defended from corrosion, but had become 
excessively ford, from the adhesion of barnacles. Several other 
vessels, so protected, have since arrived in this port ; and the 
following details will be found interesting, because they confirm 
the efficacy of the method in preserving the copper, even on 
very distant voyages ; but, at the same time, it has not uniform- 
ly prevented the adhesion of parasitic shell-fish, as has been al- 
leged. Indeed the slightest effect does not appear to have been 
produced in some instances on these animals, by the current of 
negative electricity. 
The explanation of the uncommon foulness of the bottom of the 
Tickler attempted in the Annals of Philosophy , will not apply to 
all the cases now to be detailed : for in some, on the principle there 
maintained, the copper was over defended, yetthe bottom remained 
quite clean ; while others, under similiar circumstances, were so 
covered with barnacles, as to be seriously impeded in their 
