830 
Dr Traill on Sir H. Davy's Method of 
able iron, fastened on each side of her keel, by copper spikes. 
The iron covered about / 0 th of the surface of her copper. 
This is an instance of a ship supposed to be over defended, 
yet remaining clean, in a place very favourable to the adhesion 
of barnacles and weeds. 
The Elizabeth , a vessel defended exactly in the same manner, 
and by metals in the same proportions, made the same voyage. 
Both ships had been newly coppered when they left Liverpool ; 
and the Elizabeth’s copper appeared equally clean as that of 
the Huskisson, when unloaded ; but as she did not enter the 
graving docks, it is not absolutely certain that she was quite 
clean ; especially as the Dorothy, about to be mentioned, ap- 
peared equally so, until she was viewed in the graving-dock, 
when her bottom was found to be uncommonly foul below the 
bilge. We believe, however, that the copper of the Huskisson 
was perfectly clean, as was proved in the case of the bottom of 
the Dee , a very large vessel, belonging to my relative Mr Sand- 
bach. This ship was newly coppered about twelve months ago, 
and a bar of malleable iron, about Jths of an inch thick, and 3 
inches broad, was fastened, on each side of the keel, with iron 
spike-nails. The iron covered about ^ 5 th of the copper surface. 
Since that period she has made two voyages to and from Deme- 
rara ; and, at the conclusion of the last, was put into a graving 
dock, when her copper was found to be perfectly free from 
corrosion, and almost entirely clear of adhering substances, ex- 
cept a few very small barnacles near the keel, fore and aft. 
This instance (as well as the Huskisson) shews, that over de- 
fence cannot be alleged as the cause of the foulness of a ship’s 
bottom, for both of these vessels had a much greater proportion 
of iron to their copper than the Tickler, when the bottom was 
covered by large barnacles. The iron spikes, employed to 
fasten the bars of iron on the keel of the Dee, were so much 
corroded as to endanger the falling off of the bars. Copper 
spikes are thus certainly much to be preferred for this purpose. 
The Dorothy , a fine ship belonging to Mr Horsfall and Sir 
John Tobin, had, since the application of Sir H. Davy’s pro- 
tectors, made a voyage to Bombay and back. The copper was 
