1872.] 



f Shearwater 1 Scientific Researches. 



605 



nize the importance, so long as they " remained under the dominant idea 

 " that the Temperature of the Deep Sea is everywhere 39°." Now, since 

 in my previous Report of the 'Lightning' Expedition for 1868, I had 

 specially drawn attention to the prevalent error of regarding the tempera- 

 ture of 39° as that of the Deep Sea generally (showing that it is not 

 that of the greatest density of Sea-water, which contracts until it freezes), 

 and had demonstrated the non-existence of the supposed line of equal 

 temperature at all depths, separating the Polar sea, in which the tempe- 

 rature rises with increase of depth, from the Equatorial, in which it sinks, 

 I cannot but feel greatly surprised at finding these errors repeated by 

 Dr. Petermann, as well as by his coadjutors Drs. Von Preeden and Miihry, 

 and determining their interpretation of many of the phenomena which 

 they bring under discussion. Thus Dr. Petermann says of the Gulf-stream 

 that " after coming forth intact from its two struggles with the Polar Stream 

 " east of Newfoundland and east of Iceland, its waters cool more and 

 " more towards the north, until they are reduced to a temperature of 39°*2, 

 " at which they attain their highest density and greatest loeight. At this 

 " temperature it sinks beneath the Polar Stream, in July, north of Iceland 

 " and Spitzbergen, and on both sides of Bear Island .... North of the iso- 

 " thermal curve of 39°'2 toward the Pole, the temperature generally in- 

 " creases with the depth, while southward towards the Equator it decreases." 

 — And Dr. Von Preeden says, — <c It has been established beyond doubt, by 

 " late investigations on the high seas, that Sea- water reaches its maximum 

 " density, or in other words its greatest Specific Gravity, in exactly the 

 " same manner as fresh water at a temperature of 3° R." Dr. Miihry, also, 

 though espousing the doctrine of a vertical circulation between Polar 

 and Equatorial waters, maintained by difference of Temperature, altogether 

 misconceives, under the influence of the error just stated, the effects of this 

 circulation. " The vertical distribution/' he says, " is regulated by the 

 " hydrothermal law, according to which sea-water, like fresh water, attains 

 " its maximum density and gravity at about 39 c, 2 Fahr. Of two streams 

 " meeting each other, one or the other, the colder or the warmer, will soon 

 "prove relatively less heavy; and this will continue its course on the 

 " surface, while the heavier will submerge, and flow underneath the lighter, 

 " provided that they cannot proceed side by side. It must and can be 

 " assumed that there is at the bottom of the Polar basin really a tempera- 

 " ture of 39°'2 or nearly so ; and that there is a gradual decrease of it to 

 " the surface, where it is 28°, the lowest temperature of flowing water, 

 " just near the point of congelation, below the floating field ice of about 

 " eight feet in thickness, which, at the top, has perhaps a temperature of 

 « _58° (-40° R.)."_« This," continues Dr. Miihry in a Note, " will be 

 " disputed by Physicists, who cling to a few contradictory experiments ; 



Nature, however, offers more correct and decisive data, which are con- 

 " firmed indisputably by the result of our inquiries into the vertical distri- 

 " bution of the Oceanic currents." And the doctrine of the uniform Deep- 



