ANNIVERSARY ADDRESS OF THE PRESIDENT. CXXXl 



filling up the Forth, to the level of 150 feet, 0"*50 : the great de- 

 flection therefore of 5" must be accounted for by some other source 

 of attraction, namely, the Pentland Hills ; andCapt. Clarke's conclu- 

 sions, who has made all the necessary calculations required for the 

 very intricate discussion of the results obtained, are, 1st, That the 

 attraction of the Pentland Hills is nearly equal at each of three 

 Stations on Arthur's Seat. 2nd, That the deflection at each of the 

 three Stations, due to the attraction of Arthur's Seat, is at South 

 Station 2"-21 North; at Vertex 0"'37 South ; at North Station 2"-00 

 South ; and that the remaining 4"*88 of deflection is due to the 

 attraction of the Pentland Hills. 3rd, Of the 4"-88 of deflection 2"-5 

 may be considered due to the attraction of the ground within a radius 

 of 15 miles, and that the difference between the observed and com- 

 puted attraction may be due to the high specific gravity of the mass 

 of rock beneath Arthur's Seat and the Pentland Hills ; — I may indeed 

 observe that 2" '5 appears a rather low specific gravity for igneous 

 rocks of a basaltic type. 4th, That the latitude of Arthur's Seat 

 varies 0"'02 from the difference of attraction consequent on the change 

 of level from low to high water. 5th, That the mean density of the 

 earth as deduced from these calculations is 5"'3] 6; being above that 

 deduced from the Schehallien experiments, or 5""0, and below that 

 obtained by other experiments, the late pendulum-observations of the 

 Astronomer Royal having carried it as high as 6" '5 7. 



It appears to me right to notice here the very interesting researches 

 made by the Coast Survey of the United States, and published under 

 the authority of the Government in the American Journal of Science 

 by Professor A. D. Bache, Superintendent of that Survey, which 

 relate to the distribution of temperature in and near the Gulf-stream, 

 the results being exhibited in diagrams by the system of curves. 

 The first of these represents the varying temperature with depth ; and, 

 though the rate of diminution cannot be thoroughly understood 

 without inspection of the diagram, I may state that at the surface 

 the temperature is 82°, and at 700 fathoms 38°. Several other 

 diagrams represent the temperature at the same depth, in sections 

 across the Gulf-stream, and exhibit some remarkable phsenomena ; 

 namely, — 1st, that the Gulf-stream is limited laterally by cold water, 

 the passage from one to the other being so abrupt, that the boundary 

 of cold water has been called "The Cold Wall." 2nd, That there 

 is a considerable oscillation up and down of the lines of equal tem- 

 perature ; and that, as these variations are permanent, having been 

 observed in several successive seasons, the Gulf-stream appears to be 

 divided into several bands, with intermediate streaks of colder water. 



The section through the Gulf-stream, off Charleston, is the most 

 illustrative of these facts ; and, as this section is almost entirely 

 within soundings, it illustrates another curious fact, namely, that the 

 oscillations of the lines of equal temperature appear to be influenced 

 by the form of the bottom. Thus, for example, the bottom slopes 

 gradually for fifty miles, reaching a depth of about 20 fathoms ; 

 then more rapidly for sixty-five, to a depth of 100 fathoms, when 

 it suddenly falls to a depth of more than 600 fathoms. At 100 



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