IU8 DR ALEXANDER BUCHAN ON 



observed on board the " No vara," could not be utilised, since the temperature of the sub- 

 surface water was not recorded along with the specific gravities. 



An. examination of the observations which are available shows that the number is 

 sufficient to represent important sections of the ocean only at depths of 100, 200, 300, 

 400, 800, and from 1500 fathoms to the bottom, Maps 2 to 8 ; the number at other 

 depths are al together insufficient to represent any considerable portion of the ocean which 

 could cast additional light on oceanic circulation. Thus, at 500 fathoms there are only 

 11 observations; only 6 at 600 fathoms; and even at 1000 fathoms the number is 

 only 7. Hence it is impossible yet to attempt to represent the specific gravity of the 

 ocean at any other depths than those dealt with, even over comparatively limited 

 areas. 



Since in constructing Map 1 the data employed are fairly good annual means, the 

 mean specific gravity of the surface of the ocean may be represented by coloured shadings 

 of red and blue, according as above or below the mean specific gravity of all the oceans 

 taken together, or 1"0252. But, as regards all the other maps, the observations are too 

 few, and, with reference to the different expeditions, are necessarily disposed in lines and 

 not in a scattered manner over the different oceans traversed. It has therefore been 

 judged expedient to represent the results not by lines, but only the actual observations 

 themselves. These are given in the form of differences from the simple mean of the whole 

 observations made at the depth represented by each map. When the differences are 

 above this mean the figures are red, but when under it they are blue. Thus, at 100 

 fathoms the mean of all the observations is 1*0261 ; if, then, 14 in red ink is entered on 

 the map at any point, the specific gravity there is 1*0275 ; but if it is entered as 17 in 

 black ink, then it is 1*0244. In this way the maps represent the actual state of our 

 knowledge at present ; and what is of the utmost importance, they show us in a most 

 impressive manner the enormous tracts of the ocean for which we have absolutely no 

 observations— in other words, of which we possess no real knowledge. 



The following are the more important of these enormous blanks in the ocean at 

 depths of 100 fathoms and lower : — The whole of the North Atlantic between long. 10° 

 and GO °W. to the north of lat. 40° N. is not represented by a single observation — a state 

 of matters not creditable to this country. For some considerable distance to the east of 

 the United States, the whole of the Gulf of Mexico, the Caribbean Sea, and an immense 

 region to the south-east, from lat. 20° N. to South America, as far to eastward as 

 long. 30° W. — a region whose importance in this inquiry it is impossible to over-estimate 

 — are enormous blanks, not creditable to the Governments of the United States, Great 

 Britain, and Brazil. If we except the observations of the " Gazelle " at 100 fathoms and 

 at the bottom, and Admiral Makaroff's down to 437 fathoms, the whole of the Indian 

 Ocean presents an unrelieved blank, an ocean so very important in the inquiry, seeing 

 ( li.it it is a closed ocean north of lat. 25° N. The Pacific Ocean is unrepresented 

 to the north of lat. 40° N. and east of long. 170° E., and also to the east of a line 

 drawn from about lat. 35° N. and long. 155° W. to lat. 30° S. and long. 130° W. Except 



