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In painting, distemper is a preparation of opaque colour mixed in a watery glue, such as size, eggwhite or gum. It was used chiefly in scene-painting and in paper for walls during the 19th ecntury, but was employed in the higher departments of art before the introduction of oil-painting in the 16th century. Distemper is painted on a dry surface, fresco on wet mortar or plaster.
 Research Distemper
Glaciers are icy masses of great bulk, harder than snow, yet not exactly like common ice, which cover the summits and sides of mountains above the snow-line. They are found in Switzerland, Scandinavia, the Andes, etc.
They extend down into the valleys often far below the snow-line, and bear a considerable resemblance to a frozen torrent. They take their origin in the higher valleys, where they are formed by the congelation and compression of masses of snow in that condition called by French writers neve, by German authors, firn.
The ice of glaciers differs from that produced by the freezing of still water, and is composed of thin layers filled with air-bubbles. It is likewise more brittle and less transparent. The glaciers are continually moving downwards, and not unfrequently reach the borders of cultivation. The rate at which a glacier moves generally varies from 45 to 60 cm in twenty-four hours.
At its lower end it is generally very steep and inaccessible. In its middle course it resembles a frozen stream
with an undulating surface, broken up by fissures or crevasses. As it descends it experiences a gradual diminution from the action of the sun and rain, and from the heat of the earth. Hence a phenomenon universally attendant on glaciers - the issue of a stream of ice-cold turbid water from their lower extremity. The descent of glaciers is shown by changes in the position of masses of rock at their sides and on their surface. A remarkable glacier phenomenon is that of moraines, as they are called, consisting of accumulations of stones and detritus piled up on the sides of the glacier, or scattered along the surface. They are composed of fragments of rock detached by the action of frost and other causes.
The fissures or crevasses by which glaciers are traversed are sometimes more than 30 meters in depth, and from being often covered with snow are exceedingly dangerous to travellers. One of the most famous glaciers of the Alps is the Mer de Glace, belonging to Mont Blanc, in the valley of Chamouni, about 1740 meters above sea level. It is more especially, however, in the chain of Monte Rosa that the phenomena of glaciers are exhibited in their greatest sublimity, as also in their most interesting phases from a scientific point of view.
Glaciers exist in all zones in which mountains rise above the snow-line. Those of Norway are well known, and they abound in Iceland and Spitzbergen. Hooker and other travellers gave accounts of those of the Himalaya. They are conspicuous on the Andes, while the Southern Alps of New Zealand rival in this respect the Alpine regions of Switzerland.
The problem of the descent of the glaciers is of extraordinary interest, and various theories have been put forward to account for it. It was shown by Professor Forbes, of Edinburgh, that a glacier moves very much like a river; the middle and upper parts faster than the sides and the bottom; and he showed that glacier motion was analogous to the way in which a mass of thick mortar or a quantity of pitch flows down in an inclined trough. His theory is known as the viscous theory of glaciers, which presupposes that ice is a plastic body, and this plasticity has been satisfactorily explained by Professor James Thomson of Glasgow by the phenomenon of the melting and refreezing of ice.
Water, he discovered, when subjected to pressure, freezes at a lower temperature than when the pressure is removed. Consequently when ice is subjected to pressure it melts; if it is relieved of pressure the water again solidifies. Therefore if two pieces of ice are pressed together, they tend to relieve themselves by melting at their points of contact, and the water thus produced immediately solidifies on its escape. If ice is strained in any way it similarly relieves itself at the strained parts, and a similar regelation follows. This, when applied to the glaciers, gives a complete explanation of their plasticity. Pressed downwards by the vast superincumbent mass, the ice gradually yields. Melting and re-freezing takes place at some parts, at others the gradual yielding at strained points goes on. In the latter process there is no visible melting, but there is the gradual yielding from point to point to the pressure above, and there is the transference relatively to each other of the molecules that constitute the, at first sight, solid mass. If, however, at certain points the strain is intense, the ice becomes extremely brittle. The latter fact disposes of Tyndall's objection to Forbes' theory, which was based on the fact that crevasses proved the brittleness, and not the viscosity of ice.
Research Glacier
A pestle is an instrument used for pounding and grinding substances in a mortar.
Research Pestle
Pozzolana or pozzuolana is a sort of mortar produced in Italy and formed of volcanic ashes. When mixed with a small portion of lime it quickly hardens even under water. This singular property rendered it very useful in the erection of moles and other buildings in maritime situations.
Research Pozzolana
In building, a trowel is a flat bladed tool with a short handle used for spreading mortar. A gardener's trowel is a scoop shaped tool with a short handle.
Research Trowel
David Dixon Porter was an American sailor. He was born in 1813 and died in 1891. The son of David Porter he accompanied his father in his voyages, and became a midshipman in 1829. He had served in the Mexican War, and had commanded California mail steamers, when the American Civil War called out his powers. With the control of the mortar fleet in April, 1862, he bombarded Fort Jackson and Fort St Philip, aiding David Farragut in the great feat of taking New Orleans. He was continuously active in the operations near Vicksburg that year, commanded the Mississippi squadron, and captured Arkansas Post in January, 1863.
Promoted to be rear-admiral Porter, in May, 1863, took Grand Gulf near Vicksburg and co-operated with Grant in the reduction of that stronghold. The following year he aided Banks in the Red River expedition. Transferred the same year to the North Atlantic squadron Admiral Porter commanded the powerful naval contingents in the two assaults on Fort Fisher in December, 1864, and January, 1865; in the latter, Porter and General Terry succeeded in reducing this last of the important sea fortresses left to the Confederates. He was promoted to be vice-admiral in 1866 and admiral in 1870. Until 1869 he was superintendent of the naval academy. Besides writing a life of his father and other naval works Admiral Porter was also a successful novelist.
Research David Dixon Porter
The 107mm M38 Mortar was a Soviet mortar produced as a reduced size version of the 120mm M38 Mortar for mountain troop use during the Second World War. The 107mm M38 Mortar had a minimum range of 800 metres and a maximum range of 6300 metres and a rate of fire of 15 rounds per minute.
Research 107mm M38 Mortar
The 120mm M38 Mortar was a Soviet divisional artillery mortar of the Second World War, later modified as the 120mm M43 Mortar which was still in use during the 1970's. The 120mm M38 Mortar had a minimum range of 460 metres and a maximum range of 5700 metres and a rate of fire of between 12 and 15 rounds per minute.
Research 120mm M38 Mortar
The 120 mm M1938 Mortar was a Soviet mortar of the Second World War first designed as an artillery weapon and in 1941 used as an infantry support weapon against the invading German troops. The 120 mm M1938 Mortar fired a 16 kg bomb to a range of 6000 meters.
Research 120 mm M1938 Mortar
The 160 mm Mortar M1943 is a Soviet breech-loading mortar developed from the 120mm Mortar M38 and used during the Second World War. The 160 mm Mortar M1943 has a 3030 mm long barrel and fires a 90 lb bomb to a maximum range of 5150 metres with a rate of fire of 3 rounds per minute.
Research 160 mm Mortar M1943
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The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
©1993 - 2009 The Probert Encyclopaedia
Southampton, United Kingdom
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