Transactions of the Royal Society. 343 



hand, some of the lesser features of each process are strikingly 

 apparent. We have, in fact, the presence of that which Hero- 

 dotus asserted was invariably removed in the better prepared 

 mummies, and some of those parts are absent, on the other hand, 

 which he stated never to have been touched in the inferior 

 class of those singular preparations. These facts will be duly 

 valued by the scholar, and the commentators of that historian; 

 and the explanation now given of the real mode of mummifying, 

 will enable the lexicographer to advance with confidence, that the 

 name mummy was given to such preparations from the circum- 

 stance of wax (mum in the Coptic language) being the really 

 preservative ingredient employed in their preparation." 



r. On the temporary Magnetic Effect induced in Iron Bodies by 

 Rotation. In a Letter to J. F. W. Herschel, Esq., from P. Bar- 

 low, Esq.,F.R.S. 



An abstract of the contents of this letter has appeared in our 

 thirty-eighth Number, (Vol. xix., page 263.) 



vi. Further Researches on the Preservation of Metals by Electro- 

 chemical Means. By Sir Humphry Davy, Bart., Pres. R.S. 



In two former papers (see Vol. xvii. pp. 253, 279) the Pre- 

 sident has described the effects of small quantities of electro-posi- 

 tive metals in preventing the corrosion or chemical changes of 

 copper exposed to sea- water, and has stated that the results appear 

 to be of the same kind, whether the experiments are made upon a 

 minute scale, and in confined portions of water, or on large masses, 

 and in the ocean. 



The first experiments proved, that the copper sheeting of ships 

 might be preserved by this method ; but another circumstance was 

 to be attended to, how far the cleanness of the bottom would be 

 influenced by this preservation. 



The use of the copper sheathing on the bottom of ships is two- 

 fold: First, to protect the wood from destruction by worms : and, 

 Secondly, to prevent the adhesion of weeds, barnacles, and other 

 shell-fish. No worms can penetrate the wood as long as the 

 surface of the copper remains perfect ; but when copper has been 

 applied for a certain time, a green coating forms upon it, to which 

 weeds and shell-fish adhere. When this green rust has partially 

 formed, the copper below is protected by it, and there is an unequal 

 action produced, the electrical effect of the oxide, submuriate, and 

 carbonate of copper formed, being to produce a more rapid cor- 

 rosion of the parts still exposed to sea-water ; so that the sheets 

 are often found perforated with holes in one part, and compara- 

 tively sound in other parts. 



