564 N O R N O R the Straits of Dover, and less distinctly in lines stretching from the Wash and Moray Firth to the north of Denmark. The North ; Sea lies between the January isotherms of 31 and 40, and the July isotherms of 55 and 65 Fahr., so that the difference between the mean winter and summer temperature is about 24. The temperature of the surface water ranges in January between 39 and 45 Fahr., and in July between 53 and 63. Hence the contrast between the temperature of the water and that of the air is greater in winter than in summer, and indeed except during the warmest months the air is colder than the water. In the southern part of the North Sea, south of the Dogger Bank, where the sea is comparatively shallow, there is in summer only a difference of a degree or so between the surface and the bottom water, the bottom water being a little the colder. The difference is greatest in the hollows like the "Silver Pit," where the depth reaches 45 fathoms. The tempera ture along the British coast appears to be in summer about 3 colder both at the surface and at the bottom than along the coast of Denmark. We have no very reliable informa tion as to the temperature of the water at different depths during the winter months, but we know it takes a very long time before the cooling of the surface water affects the temperature at the depth of a few fathoms, therefore it is most probable that the water at the bottom in the southern part of the sea is much warmer than the surface or intermediate water, and this is likely to be the case especially in the " pits " where the depth is greatest. This is very probably the chief reason why such large catches of soles and other fish are made in these "pits" during very cold winters. North of the Dogger Bank there is a very considerable difference of temperature between the surface and the bot tom water in summer. Off Aberdeen there is a difference of t 11, the surface temperature in summer being 56 Fahr. Fio. 1 . Distribution of temperature in the Faroe Channel. and the bottom 45, Avhile in the Norwegian gully there is a difference of 17. Farther north in the Norwegian Sea, at a depth of 300 or 400 fathoms, the water is below
- 32 Fahr. all the year round. The specific gravity ranges
FIG. 2. Section showing distribution of temperature in summer in the North Sea along a meridian line. between I 1 0249 and 1*0270, the saltest water being found at the bottom in the Norwegian gully. The lightest water is found in the Skagerrack where the Baltic water enters the North Sea, and in the southern half of the sea where the Continental rivers discharge their waters. The North Sea has an abundant flora. Algae in great abundance and variety grow on all the shores and in all the shallower waters, while a few species are found at depths of even 50 and 100 fathoms. The surface and subsurface waters swarm with Diatoms, Peridinias, Coccospheres, and other minute Algae. It is a matter of observation that where there is a low specific gravity, indicating a mixture of fresh with salt water, there is usually a great abundance of Diatomaceae in the surface waters. This is the case in bays and estuaries, and in the arctic and antarctic regions, where melting ice lowers the specific gravity. The North Sea has all the characteristic features of a great bay, and has a great abundance of plant life. Its surface or intermediate waters are at times quite discoloured by the enormous abundance of Diatoms or Peridinias which are met with in vast floating banks. The cause of the rapid and great development of these minute organisms at particular times and places appears to depend on physical conditions which are not at present understood. With such a vast food supply it is not surprising that a prolific fauna swarms in the North Sea. Everywhere on the bottom we find Foraminifera, Sponges, Ccelenterates, Echinoderms, Worms, Polyzoa, Tunicata, Molluscs, Crustacea, and Fishes. At all depths in the intermediate water we find Protozoa, Medusae, Copepods, Amphipods, Schizopods, Sagitta, and various other pelagic animals, together with a great abun dance of the larvae of animals living on the bottom. The invertebrates living on the bottom and in the water at various depths, in their adult as well as in their larval stages, supply food for those fishes which are so much de sired for the table. Most valuable food fish, as the cod, haddock, herring, sprat, holibut, sole, coal-fish, and many others, frequent the North Sea, and are captured in great numbers by the fishermen of all the nations occupying the seaboard. There are also important fisheries for crusta ceans such as lobsters, crabs, prawns, and shrimps, and for molluscs such as oysters, mussels, whelks, and periwinkles. Whales and porpoises are numerous, and sea-birds are found in vast numbers on the islands along the shores. The annual value of the North Sea fisheries of various kinds is enormous. In a recent lecture the duke of Edin burgh estimated that the labours of British fishermen supplied annually "fish food amounting to about 615,000 tons weight, which at ,12 per ton represents a money value of 7,380,000." By far the larger part of this comes from the North Sea. If we consider that these waters are also fished by Norwegians, Danes, Germans, Dutchmen, Belgians, and Frenchmen, we may form some idea of its fertility. It is very probable that the annual value of all the fisheries exceeds 25,000,000. No systematic investigation of the North Sea has yet been undertaken, and in consequence our knowledge is in many respects very meagre. This is all the more astonishing when we remember the value of the fisheries and the enterprise of the nations engaging in them. The Admiralty employed a ship for several seasons to examine the currents and tides ; the results are published in the North Sea pilot and admiralty tide tables. The German ship " Pom- merania " was engaged during the year 1872 in examining the North Sea. See Die Expedition zurphysicalisch-chemischenundbiologischen Untcrsuchung der Nordsee im Sommcr 1872 (Berlin, 1875). (J. MU.) NOETHUMBERLAND, the northernmost county of Plate England, is of a somewhat triangular form, roughly re- XIX - sembling that of England itself. It lies between 54 47 and 55 46 N. lat. and 1 25 and 2 41 W. long., and is in its extremes about 70 miles long and 53 broad. Its area is 2016 square miles, ranking it fifth among English counties. Northumberland lies entirely on the easterly slope of the country. Its boundaries are the German Ocean, Scotland, and the counties of Cumberland and Durham. In physical aspect it is a tumbled incline of fells and ridges, intersected by valleys and subsiding eastwards from the hill- borders of Scotland and Cumberland into lessening undulations and a shelving coast. The Cheviot range (separating Northumberland from Scotland) is divided by
