448 



Part III — Seventh Annual Report 



entrance to the Cromarty Firth, Stations I. and IT. where they ranged 

 from 39°*7 F. at the surface to 41°'3 at the bottom. At Station III. the 

 temperature was found to be distinctly higher, and ranged from 42° -2 F. 

 at the surface to 42° -7 at the bottom. Further out to sea the tempera- 

 tures were still higher, and also more uniform from surface to bottom. 

 At Smith Bank the range of temperature from surface to bottom was from 

 43°"3 to 43°*9 and was slightly higher at Station VIII., a few miles further 

 out to sea. The density at constant temperature is lowest between the 

 Sutors 1024-2 to 1024-5 ( 4 S ]5 . 5(3 ), distinctly higher at Station III. 1025-6 

 to 1025 - 7 ( 4 S 15 . 56 ), equally high and very uniform at Stations IV. to VII. 

 and highest at Station VIII., where the influence of the land water is 

 almost inappreciable. 



At Station III. the lowering of the density, owing to admixture with 

 land water, is counterbalanced by the increase of density due to the lower 

 temperature, so that the density in situ at this point is if anything 

 slightly greater than at Smith Bank. 



On these two occasions a set of hydrometers were used which were 

 obtained from Herr Steger at Kiel in October last. These hydrometers are 

 similar to those used by the Kiel Commission, and, through the kind 

 courtesy of Professor Karsten, were compared directly with their standard 

 set of hydrometers. 



A comparison of column XIX. in Table II. with column XIII. in Table 

 V. will show that the results obtained with these hydrometers accord 

 excellently with those obtained by direct weighing. These hydrometers 

 have this great convenience that the readings require only a very simple 

 correction, which can be applied in a few seconds with the help of Pro- 

 fessor Karsten's tables, to render them comparable with each other. 



On the Chemical Composition of the Watees of the 

 North Sea. 



■ Before the publication of Forchhammer's great work it was commonly 

 supposed that the composition of sea water was subject to very consider- 

 able variation dependent upon geographical distribution, that is to say, 

 that the salts dissolved in sea water were either chemically different or that 

 their relative preparations were subject to considerable alterations, so that 

 samples of sea water collected in different localities might reasonably be 

 expected to give very different results on analysis. Forchhammer came 

 to a very different conclusion. He says : 



f It is, besides, a result of my analyses of sea water, that the differences 

 1 which occur in water from different parts of the ocean essentially regard 

 ' the proportion between all salts and water, the strength of sea water, or to 

 1 use another expression, its salinity, and not the proportion of the different 

 ' salts invicem; in other words, the difference in the proportion between 

 ' chlorine and water may be very variable, but the proportion between 

 ' chlorine and sulphuric acid, or lime, or magnesia will be found almost 

 ' invariable.' 



This important generalisation is based upon a great number of analyses of 

 samples of sea water, chiefly surface water brought from widely different 

 parts of the ocean, and subsequent researches have only tended to confirm 

 it. Forchhammer recognised, however, certain exceptions to this general 

 rule, especially in waters obtained in or near the Arctic Regions, the 

 importance and significance of which have been somewhat overlooked, and 

 there has been a tendency to assume that any differences which might exist 

 between different sea waters were so small as to be beyond the reach of 

 analysis. This, if true, would be a very serious if not insurmountable 

 obstacle to the study of oceanic circulation, as the chemical analysis of dif- 

 ferent samples of sea waters could then afford no clue as to their origin. 



