Dr Traill on the Copper-Sheathing of Ships. 327 
a part of each sheet of the copper-sheathing, further experience 
must determine ; but in giving publicity to a fact so interest- 
ing to navigation, I am sure that no other apology, than the im- 
portance of ascertaining the truth, will be necessary to the illus- 
trious author of the proposal, to whom science is already under 
deep obligations. 
Before giving Mr Horsfall’s letter, I may observe, that he is 
the intelligent owner of the vessel in question ; and with laud- 
able promptitude adopted the method, soon after its promulga- 
tion by Sir H. Davy. The proportion of surface of the pro- 
tecting metal, to that of the copper, in this instance, somewhat 
exceeds the relative proportion assigned by the philosopher ; and 
since I received Mr Horsfall’s letter, I have been informed, that 
the proportions of the iron, ascertained by measurement, were 
from to T |p, to the whole copper-surface of the ship’s bot- 
tom. Yours truly, 
Thos. Stewart Traill. 
Extract of a Letter from Charles Horsfall , Esq. to Dr Traill. 
66 Liverpool , Feb. 19. 1824. 
“ The brig Tickler arrived here from Kingston, in Jamaica, 
about three weeks ago. She had been out on the voyage from 
this port to Jamaica and back, not quite five months; previous- 
ly to her sailing she had been new coppered. Bars of cast-iron 
three inches broad, and one inch thick, covering about 100th 
part of the surface of the copper, were placed upon each side of 
the keel, from the stem to the stern, and fastened on with cop- 
per spike-nails. The Tickler went into the Graving Dock to- 
day. I attended before the water had quite left her ; and im- 
mediately on the iron on the keel being visible, I went into the 
dock to examine it. The usual crust of red rust appeared upon 
it ; but on applying a ship’s scraper to it, I found the iron 
quite soft, to the depth of nearly half an inch. A quantity was 
scraped off, which had all the appearance of black lead ; and on 
handling, it soiled the fingers in the same way that black lead 
does, and became quite hot in the space of a minute or two ; the 
inner part of the iron-bar, or that next the copper, being quite 
hard, I wrapped a small quantity in paper, and put it in my 
pocket ; and on taking it out again, in about a quarter of an 
