on the Preservation of Metals by Liectro-chemical Means. 91 
agree when carried on under precisely similar circumstances, 
must of necessity be very irregular in their results, when made 
in different seas and situations, being influenced by the degree 
of saltness, and the nature of the impregnations of the water, 
the strength of tide and of the waves, the temperature, &c. 
In examining sheets which had been defended by small 
quantities of iron in proportions under 1-250 and above 
1-1000, whether they were exposed alone, or on the sides of 
boats, there seemed to me no adhesions of Conferve, except 
in cases where the oxide of iron covered the copper imme- 
diately round the protectors; and even in these instances such 
adhesions were extremely trifling, and might be considered 
rather as the vegetations caught by the rough surface of the 
oxide of iron, than as actually growing upon it. 
Till the month of July 1824 all the experiments had been 
tried in harbour, and in comparatively still water; and though 
it could hardly be doubted that the same principles would 
prevail in cases where ships were in motion, and on the ocean, 
yet still it was desirable to determine this by direct experi- 
ment; and I took the opportunity of an expedition intended 
to ascertain some points of longitude in the North Seas, and 
which afforded me the use of a steam-boat, to make these re- 
searches. Sheets of copper carefully weighed, and with dif- 
ferent quantities of protecting metal, and some unprotected, 
were exposed upon canvass so as to be electrically insulated 
upon the bow of the steam-boat; and were weighed and ex- 
amined at different periods, after being exposed in the North 
Seas to the action of the water during the most rapid motion 
of the vessel. Very rough weather interfered with some of 
these experiments, and many of the sheets were lost, and the 
protectors of others were washed away; but the general re- 
sults were as satisfactory as if the whole series of the arrange- 
ments had been complete. It was found that undefended sheets 
of copper of a foot square lost about 6°55 grains in passing at 
a rate averaging that of eight miles an hour in twelve hours; 
but a sheet having the same surface, defended by rather less 
than 1-500, lost 5°5 grains; ‘and that like sheets defended by 
1-70th and 1-100th of malleable iron were similarly worn, and 
underwent nearly the same loss, that of two grains, in passing 
through the same space of water. Phese experiments (the re- 
sults of which were confirmed by those of others made during 
the whole of a voyage to and from Heligoland, but in which 
during the return the protectors were lost) show that motion 
does not affect the nature of the limits and quantity of the 
protecting metal; and likewise prove that, independently of 
the chemical, there is a mechanical wear of the copper in 
M 2 sailing, 
