332 Sir Humphry DAVY*sJurther researches on 
researches. Sheets of copper carefully weighed, and with 
different quanties 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 
results were as satisfactory as if the whole series of the arrange- 
ments had been compleat. 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, de- 
fended by rather less than lost 5.5 grains ; and that 
like sheets defended by and of malleable iron were 
similarly worn, and underwent nearly the same loss, that 
of two grains, in passing through the same space of water. 
These experiments (the results 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) shows 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 sailing, and which on the 
most exposed part of the ship, and in the most rapid course, 
bears a relation to it of nearly 2 to 4.55. 
I used the very delicate balance belonging to the Royal 
Society in these experiments ; the sheets of copper weighed 
between 7 and 8000 grains ; and I was fully enabled to ascer- 
