200 



Appendices to Fourth Annual Report 



familiar with Dittmar's ' Challenger' report, it will readily be seen that 

 the differences between the calculated and observed specific gravities and 

 those between the calculated and observed total halogen indicate differ- 

 ences between certain of the samples, which differences could not be 

 detected by the total halogen determination alone, or by the specific 

 gravities alone. 



Thus the samples, station 68 bottom, station 69 bottom, station 69 sur- 

 face, station 73, station 70 surface, are all characterised by a marked 

 deviation in the ratio between the density and total halogen calculated 

 and found, and vice versa. They are thus grouped together, and a 

 reference to the chart will show that these samples were all collected 

 within a limited area. 



On the other hand, the samples collected in the Beauly Basin and in 

 Spey Bay, which show a low specific gravity due to the large admixture 

 of river water, show no such deviation in the said ratio, and are in Table 

 IV. associated with samples collected at stations 20 and 21 well out to sea. 



These relations evidently require confirmation and elucidation by further 

 careful investigation, but the suggestion may be hazarded that the great 

 purity of the waters of the Spey and Ness, draining as they do a region 

 of granite and crystaU-ine schists, will account for the non-disturbance of 

 the normal ratio, while the deviation from the normal ratio in the samples 

 specified above may be caused by the water flowing into the Cromarty 

 Pirth, with the character of which I am as yet unacquainted. 



The Expedition of 1883 itself, and most certainly the physical work 

 accomplished during it, can only be regarded as purely tentative, and pre- 

 liminary to systematic work on a much larger and more exhaustive plan 

 whenever the indispensable facilities are available. The method described 

 above for the determination of specific gravities in hydrographic work 

 is sufficiently illustrated by the results detailed. 



I have every confidence that if applied to an extensive series of samples 

 collected systematically, and as far as possible simultaneously at various 

 points of importance, such as the firths and estuaries of our coasts, the 

 method I have elaborated will yield results of the greatest permanent value 

 both scientific and practical. Systematic temperature and other physical 

 observations should of course accompany the collection of samples. 



Further, the determination of the specific gravities of the sample 

 should be, in each case, supplemented by chemical investigation. 



Since 1883 the observations carried on in connection with the Scottish 

 .Marine Station, and discussed by Dr H. R. Mill * show that the conditions 

 of different river entrances as to salinity and temperature are not the 

 same. In the Firth of Forth, for instance, where the river is small com- 

 pared to the area of the sea-inlet, the curve representing salinity was 

 found to be constant at all seasons, changing its form slightly only after 

 prolonged rain. From the river the amount of dissolved salt increases at 

 first very rapidly as the sea is approached, then more and more slowly, 

 the salinity of surface and bottom at the same time approaching more and 

 more nearly to the same value. Where, as in the Spey, the river is large 

 and rapid, and there is no sea-inlet, each tide drives in and (vithdraws a 

 wedge of sea water under the river water, which remains always fresh on 

 the surface, and flows over the surface of the sea in a stream which varies 

 in direction with wind and other conditions, and only freshens the sur- 

 rounding sea-water superficially. In the Firth of Forth, temperature in 

 summer is highest and in winter lowest in the river, and falls or rises 

 steadily as the sea is approached ; in winter the surface water is colder 



See Proc. Roy, Soc. Edin. 



