516 



NA TURE 



[H/an/i ^1, 1887 



which mark the surface of obHque fracture in a similar 

 manner to those of the cleavage face. In fact, the appear- 

 ances are remarkably similar to those of aKswcuhun^i^s- 

 clivagc, described by Heim in his " Gibergsbildung" ; but 

 the observations throw no light on the remarkable radiate 

 form sometimes assumed by the structure. In a paper in 

 the same journal Mr. Joly mentions that, in examining 

 specimens of O. antiqiia and O. radiata, he detected the 

 following peculiarity : a sunken or depressed delineation 

 of one form accompanied a raised or relieved delineation 

 of the other form. Thus, if on any specimen O. antiqiia 

 appeared as a depression, on that same surface the U. 

 radiata appeared in relief. 



From this observation it appeared probable, if any 

 meaning was to be attached to the relation, that a further 



relation would be found to obtain between the mode of 

 delineation and the position in the rock. This, a further 

 examination revealed ; in this order : on the upper surface, 

 or what was most probably the surface of deposition (the 

 cleavage of the Cambrian slate of Bray Head coincides 

 generally with the plan of bedding), the O. radiata 

 appeared invariably as a depression, the O. antiqiia in 

 relief. 



When fragments were peeled off the slate, the marks 

 were found to be transmitted, or extending to the layers 

 beneath, so that lines on the upper are seen as continued 

 on the adjacent lower layer, this, too, for thicknesses 

 exceeding a millimetre. The accompanying woodcut 

 recalls the appearance of a surface of rock in which this 

 is fairly well shown. 



ON THE DISTRIBUTION OF TEMPERATURE 

 IN THE ANTARCTIC OCEAN'' 



IN the regions of the Antarctic Ocean where icebergs 

 are numerous, and where in winter the sea-water 

 freezes, the distribution of temperature in the deeper 

 layers of water is peculiar. The facts are detailed 

 in the "Challenger Narrative" (vol. i.). The general 

 result of her observations went to show that, from the 

 most southerly station, a wedge of cold water stretches 

 northwards for more than 12° of latitude, underlying 

 and overlying strata at a higher temperature than itself 

 (p. 418). 



Although the conditions and facts likely to throw light 



' Abstract of a paper read by Mr. J. Y. Buchanan before the Royal 

 Society of Edinburgh, March 21, 1887. 



upon the cause of the existence of this cold intermediate 

 or superficial stratum overlying water which at any rate 

 in its upper layers has a temperature higher than that of 

 freezing distilled water are discussed, no satisfactory 

 explanation of the phenomenon is given. One important 

 fact is noticed at page 421. "The fact that the cold 

 wedge above referred to extended north just as far as the 

 icebergs did in March 1874 points to there being some 

 connexion between the temperature and the presence of 

 melting icebergs." It is well known that icebergs consist 

 of land-ice, which is as nearly as possible pure frozen 

 water, and melts in the air at 32° F. It was thought that 

 the effect of immmersionof sucha substance in a medium 

 having a temperature y F. lower than its melting-point 

 would be to indefinitely preserve it, that in fact only the 

 lower surfaces of the icebergs large enough to reach to a 

 depth of 300 fathoms would suffer any melting at all. 

 The existence of the cold stratum was ascribed wholly to 

 the cold brine, separated from the ice on the freezing of 

 the sea-water, sinking downwards with an initial tempera- 

 ture of from 28''5 to 29° F. This cause, though existing 

 and in operation, is quite inadequate to produce the eflect 

 observed. In Dr. Otto Pettersson's admirable work "On 

 the Properties of Water and Ice," undertaken in con- 

 nexion with the work of the Vega Expedition, there is a 

 footnote at page 318 where he says: "As a thermometer 

 immersed in a mixture of snow and sea-water ivliich is 

 constantly stirred indicates — l°'8 C, we may regard this 

 as the upper limit of the freezing and the nether limit of 

 the melting temperatures of sea-water." In a review of 

 Dr. Pettersson's work in Nature (vol. xxviii. p. 417) I 

 expressed doubt of the accuracy of this observation, but 

 on repeating it I found it to be confirmed. It affords a 

 complete explanation of the cold wedge of water in the 

 Antarctic Ocean and the dependence of its thickness on 

 the range of icebergs. These enormous islands of ice, a 

 a very large proportion of which rise in tabular form to a 

 height of 200 to 300 feet above the sea, float in many 

 cases with their lower surfaces at a depth of from 250 to 

 300 fathoms. The warmer and denser water coming from 

 lower latitudes (see " Challenger Nam" vol. i. p. 428) bathes 

 these lower surfaces, the temperature of the mixture at 

 the surface of contact falls, the heat abstracted from the 

 sea-water melts a corresponding amount of the ice of the 

 iceberg, and a saline solution is produced, less salt and 

 therefore lighter than the water away from contact with 

 the iceberg, and having a temperature which depends 

 immediately on the strength of the resulting solution. 

 Being lighter than the surrounding water, this resulting 

 solution necessarily flows up along the sides of the berg 

 to the surface, and its place is taken by fresh undiluted 

 sea-water which in its turn is cooled, diluted, and trans- 

 ferred to the surface. The result is the production of a 

 most energetic engine of circulation and means of cooling 

 and equalising the temperature of the water within the 

 reach of icebergs. As there is continual renewal of the 

 ocean water brought into contact with the ice, and as its 

 composition is constant, the temperature produced is 

 practically constant, namely 2S°"S to 29°o F., or — i°7 to 

 — I°'8 C. The layer of lighter water from 50 to 80 

 fathoms thick at the surface is due principally to this 

 melting of land-ice, though it is also due in very small 

 proportion to the melting of sea-ice. 



Table siviug the temperature at which ice melts in sea-waler 

 containing different percentages of chlorine 



Temp. C. 

 Per cent. CI. 



Temp. C. 

 Per cent. CI. 



1 -040 1 • 1 3 

 i°-S i°-6 

 I '495 



1-2 13 



1222 1-313 



1-7 I'-S 



586 1-678 1-769 



1 '4 



1-404 



This table is taken from a paper on ice and brines, 

 communicated to the Royal Society of Edinburgh on 

 March 21, 18S7. 



