Rear- Admiral King on the Specific Gravilij of Sea-ivater. 523 



In order fally to test our apparatus, we have observed the action 

 effected by a coal-gas flame of constant dimensions on our apparatus 

 on chfferent days. Determinations made in June last gave the follow- 

 ing results : — 



Mean value. . 13-91 



Observations made with the constant flame placed at different 

 known distances from the insolation vessel, proved that the amount 

 of chemical action produced varied inversely as the square of the 

 distance ; and experiments made in September with tlie standard 

 flame gave results which agreed most exactly with those obtained in 

 June. From the exact agreement of these various observations we 

 are assured of the accuracy and reliability of the measurements made 

 with our instrument. 



In order to see whether the variation of the atmospheric tempera- 

 ture exerted any iuflueuce on the sensibility of the electrolytic gas, 

 we saturated the apparatus at various temperatures lying between 

 18° and 27° C, and found that the difference between the action at 

 any two temperatures lying between the above degrees was so slight, 

 that it did not exceed the unavoidable errors of experiment. 



In the next communication we shall consider the relations of the 

 interesting phenomena of photo-chemical induction. 



Dec. 11. — General Sabine, R.A., V.P. and Treasurer, in the Chair. 



The following communications were read : — 



" Observations made to ascertain the Specific Gravity of Sea-water 

 in the Northern and Southern Hemispheres." By Rear-Adniiral 

 Phihp P. King, R.N., F.R.S. &c. 



The specimens of sea-water experimented upon were collected 

 during the voyage of Her Majesty's Ship 'Adventure,' commencing at 

 Rio de Janeiro, and from thence in succession to St. Catharine's, the 

 River Plate, round the Falkland Islands to Cape Horn, and thence to 

 Valparaiso ; and during the ship's return from Valparaiso, through 

 the Strait of Magalhaens to the River Plate and Rio de Janeiro. 

 The series was then completed by the voyage to England. 



From the author's observations it may be inferred that the density 

 of the water of the Ocean is, very nearly, identical in all j)arts of the 

 Atlantic between 40° North and 40° South latitude, the exceptions 

 being due to local causes. Dry winds, by incieasing the effect of 

 evaporation, would naturally increase the density of the sm-facc water, 

 whilst on the other hand, winds charged with vapour would have but 

 little effect ; and a heavy fall of rain, particularlv in e(puUuriaI parts 

 5i N 2 



