Lakes are accumulations of water in hollows on the earth's surface. When they are drained by rivers their waters are fresh, but when they have no outlet they are salty, e.g. the Dead Sea, Sea of Aral, etc.
Lakes may owe their origin to:
Barriers across a river valley hold back the water, which forms a lake. Such barriers may be of various types. (a) Sometimes artificial barriers of concrete and masonry are built across a valley so as to make a lake which can act as a reservoir for the water-supply of a large city, e.g. LakeVyrnwy for Liverpool. (b) A glacier may deposit a mass of morainic material across a valley. In this way the lakes of the Lake District and many of the Scottish lakes were formed. (c) A landslip may occur. A lake was formed thus in the Upper GangesValley in 1892. Two years later the landslip dam gave way, and disastrous floods occurred downstream. (d) Oxbow lakes are formed from the meanders of rivers. The deposition of silt at the two ends of the 'oxbow' closes the channel between the main river and its old loop. Many oxbow lakes border the River Murray in Australia, and the lower Mississippi. (e) Sometimes a lavastream may flow across a valley and cause the formation of a lake, e.g. LakeTaupo in New Zealand. (f) Sometimes large estuaries are partially filled with silt. In the portions not so filled are large shallow lagoons. Such lagoons are found in deltaic areas. The NorfolkBroads are portions of an old river estuary. (g) When a silt-laden stream enters a lake its speed is checked and a barrier or delta is built across the lake splitting it into two portions. This has happened in the Lake District, where Keswick stands in the alluvial flats between Lakes Bassenthwaite and Derwentwater, and in Switzerland, where Interlaken is situated in the flats between Lakes Thun and Brienz. (h) The action of the sea often causes an accumulation of sand and pebbles which cuts off a lagoon of sea water. The Fleet in Dorset is such a lagoon, cut off from the sea by Chesil Bank, a long pebble beach which joins Portland Island to the mainland.
The nehrungs of East Prussia are sand-spits which enclose the shallow salt-water lagoons or halls, such as Kurische Haff. Earth movements cause lakeformation when subsidence occurs. This is most easily seen in rift valleys. Examples of riftvalley lakes are the Dead Sea, Lakes Nyasa and Tanganyika in Africa, and LakeTorrens in Australia. These are all long, narrow, and very deep lakes.
In Cheshire, the removal of underground beds of salt has caused subsidence resulting in the 'meres' of the Weaver Valley. The 'folding' of the earth across the line of a river valley may partially block a river and help to form a lake. The study of a good physical map will reveal the connection between mountain building and the formation of LakeGeneva and LakeConstance in Switzerland. Where there are large areas of depressed lowland wide and shallow lakes are formed in the lowest part of the depression, for example the Sea of Aral in Asiatic Russia, LakeBalaton in Hungary, and LakeEyre in Australia. Ice sheets and valley glaciers may scoop out hollows to form 'rock basins'. Mountain tarns and corrie lakes in North Wales and Scotland have been formed in this way. Water also accumulates in the hollows of unevenly- distributed glacial drift. Such are the lakes of East Prussia, and also those of the Cheshire-Shropshire borders near Ellesmere. Subsidence of the land surface and consequent lakeformation may be directly related to volcanic action. Lough Neagh in Northern Ireland is a shallow lake formed by subsidence of this type. Lakes are often formed by the accumulation of water in the craters of extinct volcanoes, for example the Laachersee in the Eifel region of Germany. Research Lakes
The Garden Pebble (Evergestis forficalis) is a moth of the family Pyralidae with a wing span of between 25 and 28 mm found in temperate Europe, Asia and North America in habitats of lush vegetation. Two generations are produced flying from May to September. Research Garden Pebble
The Pebble Hook-tip (Drepana falcataria) is a moth of the family Drepanidae with a wing span of between 27 and 35 mm found in central and northern Europe flying in two generations from April to June and July to August. Research Pebble Hook-Tip
The Pebble Prominent (Eligmodonta ziczac) is a moth of the family Notodontidae with a wing span of between 40 and 45 mm found in Europe and Asia in damp deciduous forests, overgrown hillsides and in urban parks. Two generations are produced flying from April to August. In mountainous environments, a single generation is produced. Research Pebble Prominent
In Inuit mythology, Eeyeekalduk is a god of healing. He is depicted as a tiny old man, whose face was a speck of jet and who lived inside a pebble. He cured people by looking at them, drawing the sickness out along his line of sight. Research Eeyeekalduk
Gunpowder is an explosive mixture of potassium nitrate, charcoal and sulphur in the proportions of 75, 15 and 10 - although alternative proportions are also used. The three ingredients must be very finely ground and mixed, and ordinary charcoal is not very suitable. Rather charcoal from dogwood, alder or willow is used. The wood is cut in spring and stored for between two and three years before being cut into small pieces and packed into thick iron containers with holes at one end to allow gases to escape, and heated for four hours.
The crude pottassium nitrate is dissolved in boiling water, filtered, and then allowed to cool and crystallize in a trough in order to purify it from nitrates of soda and lime, chlorides of potassium and sodium, etc, the liquid being continually agitated, so that the crystals may be formed small and pure. They are then washed and allowed to drain. The sulphur is purified and ground. The charcoal is obtained from alder or willow wood, or from dogwood for the finest powder. These ingredients are first roughly mixed, then sprinkled with water and incorporated under rollers in a mill, and formed into a cake termed 'mill cake'. This is broken up under grooved rollers, and brought by pressure into 'press cake'. After this it is granulated, by being passed between toothed rollers, and separated into classes by sieves of different sizes of mesh. Around the end of the 19th century a very large grain was adopted for the heaviest ordnance; this was termed pellet or pebble powder. 'Pellet' powder was made by filling the cylindrical holes in a thick gun-metal plate with mealed powder, and by means of pistons under a hydraulic press, forming them into short cylinders or 'pellets', with a small cavity at one end to catch a flame the more readily. 'Pebble' powder was made by cutting or pressing edges which divide the press cake into small cubes; these, like pebbles, have their corners rubbed off and rounded by friction. The largest pebble powder consisted of cubes of 1.5 inches.
There is also a gunpowder known as 'prismatic', the grains forming large hexagonal prisms with a hole through the centre. 'Cocoa' powders are made with other kinds of carbon than wood charcoal. The greatest precautions must be taken to prevent fire or water from coming into contact with gunpowder. Hence it was usually kept in magazines which were of great strength in defensive works, although lighter and well-ventilated buildings sufficed under other conditions. In the transportation of gunpowder, the casks should be dust-proof, and the carriages and vessels containing it should be water-tight. As iron vessels are dangerous, gunpowder was usually packed in copper-hooped barrels made with coppernails.
The explosive power of gunpowder is very great. It is, however, necessary to place it within a confined space, as, when it is heaped up in the open air, it explodes without report or much effect. As the result of experiments it appears that the weight of the gases produced by inflaming gunpowder is about three-fifths of that of the powder, and their volume 288 times its bulk, when they have attained an elasticity equal to that of the air. If the effect of heat evolved during the combustion be added, the elastic force is increased to 1000 atmospheres in round numbers, i.e. a pressure of about 6.5 tons to the square inch.
Gunpowder is thought to have been invented by the Chinese and Marcus Graecus, who lived about the 9th century, describes its composition, which was also known to Roger Bacon, who refers to it in 1267. It was also apparently known to the Arabs at an early period. In 1342 the Moors employed it in the siege of Algeciras. According to the common story the discovery of its propulsive power was due to the German monk Barthold Schwartz between 1290 and 1320.
Guns are said to have been employed by Edward III in 1327, on his invasion of Scotland. It is also asserted that gunpowder was employed in 1346 by the English at Crecy. It was not, however, until the 16th century that its use in warfare became general.
The Sud-Est SE.5000 Baroudeur was a French single-seater jet fighter aircraft of the 1950's, first flown in 1953, and designed to operate independently of airfields with long runways, such as uncultivated fields, sand and pebble beeches and muddy or frozen ground. To this end, take off was achieved with the use of a three-wheeled trolley and landing took place on skids. The Sud-Est SE.5000 was a shoulder-wing cantilever monoplane with swept-back wings powered by a SNECMA Atar 101 axial-flow turbojet engine. Research Sud-Est SE.5000
Abbreviations
Research Lakes
