714 REPORT — 1894. 



the Norwegian Sea lyiug at the bottom of the Faeroe-Shetland Channel, and loses 

 its horizontal motion. The warmer the Atlantic current, the more rapidly does 

 this mixture take place. Hence in a hot, windless summer a mass of Atlantic 

 water, extending to a great depth, tends to collect on the northern and north- 

 western edge of the North Sea bank. 



2. At all seasons Atlantic water is drawn from the Faeroe-Shetland Channel 

 and forced into the North Sea by the tides between Orkney and Shetland. The 

 tidal streams run N. W. and S.E., and an eddy is formed to the north-west of the 

 Orkneys, into which North Sea water is drawn, and perhaps also water from 

 below. 



3. As the season advances the surface water of the North Sea becomes warmer, 

 the upper layers probably receive smaller supplies of fresh water, but they become 

 specifically lighter than the under layers, which they protect from the warming 

 influences of tlie atmosphere. The upper layers becoming idtimately warmer 

 than the Atlantic current, the surface of the North Sea becomes higher, and the 

 surface water spreads outwards into the Faeroe-Shetland Channel, checking the 

 surface supply of Atlantic water. 



Meanwhile, the mass of Atlantic water, collecting at the edge of the North Sea 

 Bank, seeks entrance into the North Sea. Mixing with the cold bottom water 

 already there, it increases its salinity, but reduces its specific gravity by warming 

 it, and, at a certain stage of mixture, the temperatures and salinities of the two 

 waters combine to form a ridge or axis of maximum specific gravity. This axis, 

 which probably ]-uns N.E. from Shetland in the end of May or in June, turns 

 slowly toward a N. to S. direction, and moves eastward. As it retreats, Atlantic 

 water is gradually admitted round the north end of the Shetlands, passes down 

 the east side of the groups, joins the tidal stream at the south end, and, guided by 

 the axis of heavy water, is distributed along the east coast of Scotland, probably 

 during July and August. Later in the summer, as the axis retreats still further, 

 the Atlantic water is probably distributed more towards the eastward, perhaps 

 imtil the latter part of September, when the diminishing supply from the Faeroe 

 Channel, and the increasing outflow from the eastern side of the North Sea, bring 

 about a gradual return to the conditions with which we started. 



Obviously the controlling conditions are complex, but it appears that the greater 

 the winter cold and the spring supply of ice-cold water from the continent, the 

 more slowly will Atlantic water penetrate into the North Sea below the surface ; 

 and the wanner the summer, the more will the surface supply be checked. At the 

 same time, the warmer the summer the larger the quantity of Atlantic water 

 seeking admission, and the greater its thermal power to drive back the axis of 

 maximum weio^ht. 



4. On Geographical rhotography. By John Thomson. 



The paper dealt with the difficulties experienced by travellers in the use of 

 photography as an aid to exploration. The purposes of photography referred to 

 did not include surveying, but merely the production of pictures showing ethno- 

 graphic types, characteristic scenery from the geographical rather than the artistic 

 point of view, and the details of artificial structures. 



The necessity of proper training in the principles as well as the practical 

 methods of photography was insisted on. Practical hints were given for the pre- 

 servation and use of dry-plates, and for the successful development of negatives in 

 tropical countries. 



A series of travellers' photographs illustrating the excellences and the defects 

 of such work was shown by the lantern. 



