56 A Retrospect of Oceanography 



commonly used by all seafaring people is very apparent. The 

 units of distance still in use on board the ships of all nations 

 is the nautical mile, which is the length of a minute of arc 

 on the meridian at the place. The unit of depth used by 

 all nations except the French up to the last eight or ten years 

 was the fathom, and the British fathom, for all purposes 

 of comparing depth with distance, is the -j-^oo part of a nautical 

 mile. More nearly, 1010 fathoms go to the nautical mile, 

 so that a correction of one per cent, is all that is required 

 for work of great accuracy. In the work which we have been 

 describing, 10 fathoms is a small fraction of the ship's length, 

 and accuracy to that extent cannot be guaranteed. The 

 difference of depth in fathoms per nautical mile of distance 

 gives at once the tangent of the slope. Using nautical miles 

 for distance and metres for depth is exceedingly inconvenient, 

 and only produces confusion. Up to the year 1880, all the 

 oceanographical work that had been published was expressed in 

 terms of the nautical mile and English fathom, and at the present 

 day quite nine-tenths of what has been done has been done with 

 the fathom. It is a very great pity that continental nations, 

 other than France, should introduce confusion by using a new 

 unit of depth, and one which has no simple relation with the 

 unit of distance. As an example of the great convenience 

 of the fathom and nautical mile, the report on the magnificent 

 work of the U.S. S. "Albatross," between California and the 

 Sandwich islands, published at Washington in 1892, may be 

 cited. 



The routine chemical work on the "Challenger" consisted 

 in boiling out the atmospheric gases, and determining the 

 carbonic acid in as many samples of water as possible. The 

 apparatus for boiling out the gases was the same as that 

 used and described by Professor Jacobsen, to whose visit 

 to Leith in the "Pomerania" I was indebted for many useful 

 hints. The apparatus for determining the carbonic acid 

 differed from his in some details. He boiled down the water 

 to very near dryness, collecting the distilled water and evolved 

 carbonic acid in a receiver holding baryta water. Dr Jacobsen 

 told me at the time that there was danger in his method of 



