Mr. F. Field on the Existence of Silver in Sea-water. 525 



none of the original on board. A piece of yellow metal with which 

 he was repairing the Tessel yielded only oz. 18 dwts. to the ton. 

 I was enabled by the courtesy of the captain of the ' Nina,' a brig 

 which had just arrived in the Pacific from England, to obtain more 

 satisfactory information. He gave me a piece of Muntz's yellow 

 metal from his cabin, from the same lot with whicli the brio- was 

 sheathed, but which had never been in contact with salt water ; and 

 also a small portion from the hull of the ship after it had been on 

 nearly three years. The experiments were performed as before, and 

 the results were very striking. 



g^s- gr- oz. dwts. grs. 



1 700 from cabin gave -051 =-003 per cent.=0 19 14 per ton. 

 1700 from hull „ ■400 = -023 „ =7 13 1 



That which had been exposed to the sea having nearly eight times as 

 much silver as the original sample. 



Many other specimens were examined of metals from the bottoms 

 of ships, and of pieces which are always kept on board in case of 

 need, and it was invariably found that the former contained more 

 silver than the latter. For instance, a piece from the hull of the 

 'Bergmann' gave 5 ozs. 16 dwts. 18 grs. per ton, while that from 

 the cabin yielded 4 ozs. 6 dwts. 12 grs. 200 grs. from a piece from 

 the hull of the ' Parga' gave '072 gr., and a piece of fresh metal 

 •050 ; while from the ' Grasmere,' only coppered a few months, 

 610 grs. from the hull gave -075 and from the cabin "072, — a very 

 shght difference indeed. 



It will be observed that the amount of silver in the above specimens 

 of fresh metal is very high, and it is probable that most of these are 

 merely the re-rolUng of masses of metal melted down from old 

 sheathing, and have derived the greater part of their silver from the 

 sea on former occasions. It is well known that the copper used in the 

 manufacture of yellow metal is very pure, containing 2 or 3 dwts. of 

 silver per ton, frequently not so much, and silver is very seldom asso- 

 ciated with the other constituent, zinc. In order to arrive at more 

 certain results, however, I have granulated some very pure copper, 

 reserving some in a glass stoppered bottle, and suspended the 

 remainder (about 10 ounces) in a wooden box perforated on all sides, 

 a few feet under the surface of the Pacific Ocean. When occasion 

 offers, the box is towed by a line at the stern of a vessel which is 

 trading up and down the coast of Chili. It is almost too soon to 

 expect any decisive results at present, but in a few mouths I hope 

 to be enabled to send both the original copper, and that which has 

 been exposed to the action of the sea. 



" On the Causes of the great Variation among the different 

 Measures of the Earth's Mean Density." By Captain W. S. Jacob, 

 Director of the Observatory at Madras. 



The result of the Pendulum experiments in the Harton Colliery, 

 undertaken by the Astronomer Royal in 1854, and detailed in his 

 paper presented to the Royal Society in January 1856, apjjcars at 

 first sight rather startling, as adding to the already somewhat dis- 



