i895. RESULTS OF '^CHALLENGER'' EXPEDITION. 13 



depth of each 100 fathoms from the surface to the bottom, and at 

 every 10 fathoms to a depth of 200 fathoms, enabled diagrams to be 

 constructed showing the vertical distribution of temperature in all the 

 great ocean basins. These determinations furnished a standard of 

 reference for subsequent observations, which have confirmed, in a 

 remarkable manner, the results of the " Challenger " Expedition, and 

 have shown that, at depths exceeding 100 fathoms, the temperature 

 is either constant, or the change is so small that it cannot be 

 recorded in a period of twenty years. 



4. Early in the voyage it was remarked that over certain areas 

 the bottom temperature remained constant. Thus, in the eastern 

 part of the North Atlantic the temperature at all depths exceeding 2,000 

 fathoms was constant at 36-8° Fahr., whilst in the western part it was 

 o*5° lower. Subsequent experience in the North Pacific showed that 

 the bottom temperature was constant at 35° ; in the China Sea it was 

 36-8° ; in the Sulu Sea, 50-5° ; in the Celebes Sea, 387° ; and in the 

 Arafura Sea, 38*6° ; whilst in the south-western part of the South 

 Atlantic the temperature at the bottom fell to 32'7° — and previous 

 results obtained in the " Porcupine " gave a minimum of under 30° 

 for the bottom temperature to the north-eastward of the Faeroe 

 Islands in the North Atlantic. These results were finally shown 

 to be caused by certain oceanic areas being separated from each other 

 by submarine ridges, which prevent the spreading to low latitudes of 

 the cold bottom water existing in, or near, the polar basins. 



In connection with these results it is worth noticing that no 

 bottom temperature was obtained as low as the freezing point of salt 

 water, and that the only temperature hitherto recorded which is near 

 the point of maximum density of sea-water (25'4°) is that obtained in 

 the voyage of Sir John Ross to the Arctic in 18 18. Also that the 

 bottom temperature of the Red Sea is constant at 6g°, and of the 

 Mediterranean at 55^-°. 



5. The " Challenger " was provided with twelve chronometers, 

 and careful observations were made at each place touched at, and the 

 meridian distance between each place calculated. The longitude of 

 some of the islands in the Southern Indian Ocean was proved to be 

 twenty minutes or upwards in error. The total of the 'meridian 

 distances round the world amounted to 360° 7' — an error of seven 

 minutes in a voyage lasting three-and-a-half years, during which the 

 chronometers had been exposed to great differences of temperature, 

 and the length of time occupied between the ports had necessarily 

 been much lengthened in order that the special work of ocean 

 exploration might be properly performed. 



6. Although the " Challenger " was not specially employed for 

 surveying work, advantage was taken of the vessel's stay at any 

 port to survey the anchorage, or add to the chart already existing. 

 Thus, in the course of the voyage, an elaborate survey was made of 

 the space enclosed by the mole at Gibraltar, plans were made of 



