250 Sir Hutnpby Davy on the [ApRit^ 



In examining sheets which had been defended by small 

 quantities of iron in proportions under -zj-i-^ and above toVo» 

 whether they were exposed alone, or on the sides of boats, there 

 seemed to me no adhesions of confervse, except in cases where 

 the oxide of iron covered the copper immediately round the 

 protectors ; and even in these instances such adhesions were 

 extremely trifling, and might be considered rather as the vege» 

 tations 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 experiment; 

 and I took the opportunity of an expedition intended to ascer- 

 tain some points of longitude in the north seas, and which 

 afforded me the use of a steam boat, to make these researches. 

 Sheets of copper carefully weighed, and with difterent 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 examined 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 arrangements 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 -^ lost b-b 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 Heligo- 

 land, 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 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- 

 tain by means of this balance, a diminution of weight upon so 

 large a quaritity, equal to -^-^ of a grain. It was evident from a 



