206 



Staff Commander T. H. lizard. 



[May 10, 



all the soundings obtained, as well as the position of the five sectional 

 lines across the ridge, and the line of demarcation between the cold 

 and warm areas, for which purpose the isotherm of 40° has been 

 selected as the best distinctive mark. The diagrams show the 

 temperature curves, and a profile of each section exhibiting the form 

 of the ridge, and the distribution of temperature from the surface to 

 the bottom. 



The diagrams all appear to point to the same conclusion, thus 

 agreeing with theory, namely, that the water is flowing steadily to the 

 north-east over the ridge. For instance, in Plate 7, Section A, it will 

 be seen that the curves of temperature begin to diverge rapidly below 

 the depth of 170 fathoms, and by referring to Plate 5, Section A, 

 it will be seen that the least depth over the ridge on this section is 

 120 fathoms. In Plate 7, Section B, it will be seen that the curves 

 taken in the warm area and on the ridge, agree very closely, whilst 

 that taken in the cold area, 10 miles north-east of the shortest cast 

 obtained on this section, 260 fathoms, begins to diverge rapidly at 

 200 fathoms from the other two curves. In Plate 7, Section C, curves 

 taken in the warm and cold areas are sensibly the same to the depth 

 of 300 fathoms, and a reference to Plate 5, Section C, will show that on 

 this section the least depth found on the ridge was 305 fathoms. In 

 sections B, D, and B, where the least water on the ridge is much the 

 same, the isotherm of 40° on each section at a distance of 10 miles 

 from the axis of the ridge, is found at almost precisely the same 

 depth, viz., 280 fathoms, or the precise depth of the ridge, whereas in 

 Section 0, where the depth of the axis of the ridge is 305 fathoms, 

 the isotherm of 40° is found at a depth of 300 fathoms in the 

 cold area, and in Section A, where the depth on the axis of the ridge 

 is 120 fathoms, the isotherm of 40° is at a depth of 250 fathoms in the 

 cold area. The depth then at which the isotherm of 40° is found in 

 the cold area depends on the depth over the ridge. As before 

 mentioned, in the warm area, all the temperatures exceed 40°. 



The question then arises, if the water is flowing steadily over the 

 Wyville Thomson ridge to the north-east, how is it the water at the 

 bottom in the cold area retains its low temperature ? This has 

 hitherto been very difficult of explanation, as there was apparently no 

 outlet for it over the ridge, and consequently we might expect that 

 its temperature would be influenced by the mass of heated water 

 above ; for the excess of inflow in the Faeroe Channel might be 

 altogether absorbed by the outflow, which we know is consfantly in 

 progress between Iceland and Greenland. The soundings and tem- 

 peratures taken this year, however, led to the discovery of a slight 

 outflow of the cold Arctic water over the deepest part of the Wyville 

 Thomson ridge, in the 7-mile gap, which breaks the continuity of 

 the 300 fathom contour-line of soundings. Here the cold water was 



