done on board H.M.S. ' Challenger/ 599 



mean specific gravity of 1-02713, that in the months of February and 

 March and mean latitude 22° N. the mean surface specific gravity is 

 1-02773, that in the month of August and mean latitude 2° N. it is 

 1-02624, and that in the month of October in mean latitude 36° S. it is 

 1-02621. 



On the way to and from Halifax in the month of May some obser- 

 vations were obtained in the cold water with which the north-eastern 

 coast of America is surrounded, the mean specific gravity being 1-02463. 

 On the 1st May in the Gulf-stream the specific gravity of the water 

 was 1-02675, and its temperature 23°*9 C. * and the next day it was 

 1-02538, and the temperature 13°-3 C. If the results be reduced to their 

 values at the respective temperatures of the different waters, we have for 

 the specific gravity of the Gulf-stream water 1*02445, and of Labrador- 

 current water 1-02584 ; so that the fall of temperature very much more 

 than counterbalances the want of salt in the water. In the same way we 

 find the mean specific gravity of the water referred to the temperature 

 which it has in the ocean to be — in latitude 36° N. and month of June 

 1-02548, in 22° N. and months of February and March 1-02592, in 2° 

 N". and month of August 1*02335, and in 36° S. and month of October 

 1-02659. 



Leaving Simon's Bay on the 17th December, 1873, the ship proceeded 

 in the direction of the Marion Islands. Immediately outside the Cape 

 the warm water of the Agulhas current was met with, which possessed a 

 comparatively high specific gravity, averaging on the 18th, 19th, and 20th 

 December 1*02657 at 15°*56 C, and 1*02477 at the average temperature 

 (21°*9 C.) of the water. As we advanced in a southerly direction, the 

 specific gravity as well as the temperature sank rapidly ; and on the 26th, 

 when off the misty and snow-capped islands of Marion and Prince 

 Edward, the surface was 5°*3 C. and the sp. gr. 1*02518. After leaving 

 these islands, and until on the way northward to Australia we had passed 

 the 50th parallel of south latitude, the specific gravity of the surface 

 remained remarkably uniform. Between the Marion Islands and Ker- 

 guelen's Land the average specific gravity was 1*02512, between Ker- 

 guelen's and the edge of the pack-ice it was 1*02506, along the 

 verge of the pack-ice it was 1*02476, and between the pack-ice 

 and the 50th parallel it was 1*02514 ; thence to the Australian coast it 

 rose daily, reaching 1*02638 off Cape Otway. Except when amongst 

 loose ice, there was hardly any variation at all in the specific gravity all 

 the way between Marion Island and the 50th parallel ; when amongst 

 the ice the specific gravity was liable to sudden and considerable fluctua- 

 tions, going down on the 14th February to 1*02419, and on the 18th to 

 1*02418, the ship being on both occasions surrounded by broken pack-ice. 

 During the same trip the specific gravity at the temperature of the water 

 was also very uniform, the mean being 1*02690. 



Leaving Sydney a loop-like course was made, by way of New Zealand, 



