Conservation of natural resources is now usually embraced in the broader conception of conserving the earth itself by protecting its capacity for self-renewal. Particularly complex are the problems of nonrenewable resources such as oil and coal (see energy, sources of) and other minerals in great demand. Current thinking also favors the protection of entire ecological regions by the creation of "biosphere reserves." Examples of such conservation areas include the Great Barrier Reef off Australia and Adirondack State Park in the United States. The importance of reconciling human use and conservation beyond the boundaries of parks has become another important issue.

Conservation in the United States

Conservation became part of U.S. government policy with the creation (1871) of a U.S. commissioner of fish and fisheries. The Forestry Bureau of the Dept. of Agriculture created the first national forest reserve in 1891. The Irrigation Division in the U.S. Geological Survey developed into the Bureau of Reclamation. The Geological Survey has cataloged and classified the resources of the public domain. In 1906 an act protected the Alaskan fisheries. Conservation as part of a total approach to the use of natural resources was first introduced by President Theodore Roosevelt and his chief forester, Gifford Pinchot. In 1907 President Roosevelt appointed the Inland Waterways Commission, which emphasized the connection between forests, water supply, and stream flow. In 1909 he appointed the National Conservation Commission, which published the first inventory of the country's natural resources. Roosevelt in 1907 began withdrawing large areas of western public land from sale and settlement so that their resources might be investigated, and setting apart forest reserves, following the example of President Cleveland. Approximately one fourth of all timberland is held by the government. The National Park Service was created in 1916 to preserve landscapes of important aesthetic value. In the 1930s the erosion of much arable land in the Midwest underscored the need for land reclamation and for conservation in general. The National Industrial Recovery Act of 1933 provided for conservation. The Civilian Conservation Corps, founded in 1933 to relieve unemployment, furnished the personnel for many conservation projects. The Tennessee Valley Authority, set up in 1933, was an outstanding attempt to apply principles of conservation, soil reclamation, and electrification to an entire area, although some critics claim that the extensive river damming and similar New Deal legislation did not, on the whole, have a positive effect on the environment. By 1960 the Soil Conservation Service, established in 1935, covered 95% of all farms and ranches in the United States. By the same year, under the Conservation Reserve Program, some 28 million acres of cropland had been returned to grass and forest cover. Throughout the 1950s attention was focused on the problem of conservation of water resources, particularly in the Southwest. In the 1960s pollution problems came to the fore in all industrialized countries. In the United States numerous laws were passed to protect the environment and its resources (see environmentalism).

Conservation Worldwide

The commitment of nations to conservation policies varies. Some nations, such as Iraq, Cambodia, and the republics of the former Soviet Union, have no protected areas, while 38% of Ecuador's land is protected and 44% of Luxembourg's is. (In the United States 7% of the land is protected.) Plants and animals have been protected through curtailment of whaling and the taking of porpoises in tuna seines and restrictions on logging. Endangered species have been protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, 1979). In addition to CITES, United Nations Conference on Environment and Development (the "Earth Summit," 1992) produced an agreement to protect the world's biological diversity. The World Wildlife Fund, Greenpeace, and other organizations also have been active in promoting conservation internationally.

Conservation of Classical Processes

Most conservation laws are exact, or absolute, i.e., they apply to all possible processes; a few conservation laws are only partial, holding for some types of processes but not for others. By the beginning of the 20th cent. physics had established conservation laws governing the following quantities: energy, mass (or matter), linear momentum, angular momentum, and electric charge. When the theory of relativity showed (1905) that mass was a form of energy, the two laws governing these quantities were combined into a single law conserving the total of mass and energy.

Conservation of Elementary Particle Properties

With the rapid development of the physics of elementary particles during the 1950s, new conservation laws were discovered that have meaning only on this subatomic level. Laws relating to the creation or annihilation of particles belonging to the baryon and lepton classes of particles have been put forward. According to these conservation laws, particles of a given group cannot be created or destroyed except in pairs, where one of the pair is an ordinary particle and the other is an antiparticle belonging to the same group. Recent work has raised the possibility that the proton, which is a type of baryon, may in fact be unstable and decay into lighter products; the postulated methods of decay would violate the conservation of baryon number. To date, however, no such decay has been observed, and it has been determined that the proton has a lifetime of at least 10³¹ years. Two partial conservation laws, governing the quantities known as strangeness and isotopic spin, have been discovered for elementary particles. Strangeness is conserved during the so-called strong interactions and the electromagnetic interactions, but not during the weak interactions associated with particle decay; isotopic spin is conserved only during the strong interactions.

Conservation of Natural Symmetries

One very important discovery has been the link between conservation laws and basic symmetries in nature. For example, empty space possesses the symmetries that it is the same at every location (homogeneity) and in every direction (isotropy); these symmetries in turn lead to the invariance principles that the laws of physics should be the same regardless of changes of position or of orientation in space. The first invariance principle implies the law of conservation of linear momentum, while the second implies conservation of angular momentum. The symmetry known as the homogeneity of time leads to the invariance principle that the laws of physics remain the same at all times, which in turn implies the law of conservation of energy. The symmetries and invariance principles underlying the other conservation laws are more complex, and some are not yet understood.

Three special conservation laws have been defined with respect to symmetries and invariance principles associated with inversion or reversal of space, time, and charge. Space inversion yields a mirror-image world where the "handedness" of particles and processes is reversed; the conserved quantity corresponding to this symmetry is called space parity, or simply parity, P. Similarly, the symmetries leading to invariance with respect to time reversal and charge conjugation (changing particles into their antiparticles) result in conservation of time parity, T, and charge parity, C. Although these three conservation laws do not hold individually for all possible processes, the combination of all three is thought to be an absolute conservation law, known as the CPT theorem, according to which if a given process occurs, then a corresponding process must also be possible in which particles are replaced by their antiparticles, the handedness of each particle is reversed, and the process proceeds in the opposite direction in time. Thus, conservation laws provide one of the keys to our understanding of the universe and its material basis.

Background

Works of art are subject to a variety of disfiguring ills, many of them caused by environmental effects, particularly temperature and humidity changes and pollution. Much modern conservation effort is directed toward producing a stable, favorable situation for the display of art works and maintaining regular inspection and diagnostic procedures to combat deterioration. Techniques for this inspection have become increasingly sophisticated; they currently involve photographic, X-ray, infrared, and other radiation examination, as well as complex chemical analysis.

All effective art conservation and restoration ultimately depend upon the restorer's understanding of materials, technical craftsmanship, and aesthetic and historical awareness. The support (such as wood panel, canvas, paper), the ground (gesso, chalk), and the surface treatment (wax, varnish) of a painting all undergo some form of decay over the years.

Support Restoration

Frescoed walls absorb moisture from the atmosphere. The moisture carries to the wall soluble surface salts that effloresce and injure the fresco pigments. To halt such injury water-permeable fixatives may be applied to help stabilize the pigment and prevent it from flaking off. A more drastic treatment is transfer, by which the mural and upper layer of plaster are cut away from the wall altogether and made fast to a new support. A major instance of successful transfer was carried out on many frescoes unearthed at Pompeii.

Wood-panel paintings undergo much swelling and shrinking with humidity variations. Wood-boring insects and the dry rot of fungus also attack them. The painting may be transferred to a new support, or the old one may be strengthened by impregnation with a consolidating medium (including several plastics) or given auxiliary support. Insecticides and fungicides may suffice to combat woodworms and dry rot; in cases of advanced destruction, reinforcement by impregnation may be necessary.

Canvas supports also absorb and lose moisture, swelling and shrinking, and thereby losing much pigment. In addition, canvases may be weakened or torn with comparative ease. A method of relining (restretching on a second undercanvas) may be effected whereby the old canvas is attached to the new by means of an adhesive. This may be a thermoplastic wax-resin combination or a water-base glue. The painted surface becomes impregnated with the adhesive and is consequently stabilized.

Irregular staining, called foxing, is the bane of print and drawing collectors. In humid conditions foxing attacks the adhesives and mounts of paper-based art, including watercolors, by producing the nutrients favored by molds present in the atmosphere. The work may sometimes be sterilized and remounted on a support chosen for its mold-repellent quality. It may be further treated with a fungicide. Some foxing stains may be removed by careful bleaching and washing, but this is a difficult technique requiring considerable knowledge of materials.

Ground Restoration

Repainting and retouching are means by which a damaged work may be restored, but both largely depend for success upon the personal judgment and aesthetic capability of the restorer. Repairs may be necessary where the results of overzealous cleanings of the past have produced injury or revealed a pentimento that disrupts the composition. Much of the restorative work of the 19th cent. had a tendency to "improve" the work of art with arbitrary additions and distortions, and a good deal of 20th-century attention was given to removing these additions.

Surface Restoration

The restorer's greatest problems concern the surface coating of the painting. A decayed or badly discolored varnish may be removed painstakingly by mechanical means or regelled with the judicious use of solvent, often applied as a delicate spray. In other cases the old varnish may be powdered by rubbing and removed by hand or, more commonly, chemically dissolved. Such techniques are beset by dangers inherent in the variable nature of the original pigments and varnish, and the risk of injury increases with the age of the painting. When a new varnish is applied, the contemporary restorer uses a much more easily removed surface protector than was common in the past.

Restoration of Sculpture

Sculpture, especially that which stands outdoors, is particularly vulnerable to environmental changes. Placing the sculpture in a temperature- and humidity-controlled situation is the best means by which to preserve it. Stone sculpture requires periodic washing; either steam, spray, or trickled water is used, depending on the porosity of the stone. Soap, but not detergent, may also be applied. Broken sculptures may be mended with clear, cold-setting adhesives, sometimes mixed with a suitably colored filler, or by means of dowelling. Large pieces of sculpture are held together with metal dowels, usually of copper, stainless steel, or brass.

Broken wood sculpture is also dowelled, as is ivory, and special cements may also be used to fill cracks. Wood sculpture is also vulnerable to woodworm and dry rot and may be treated with insecticide and fungicide. Badly decayed wood works may sometimes be preserved by means of impregnation with a plastic medium.

Metal sculpture may be waxed to protect it from atmospheric corrosives. Bronze acquires a patina, or irregular surface pattern caused by deposits of sulfides and oxides, that is widely considered aesthetically pleasing, whereas patina on lead objects results in eventual decay. Cracks in metal sculpture may be filled with special adhesives. Corrosion may be halted by electrolytic reduction, which, however, destroys patina. Various chemical solvents and mechanical techniques are used to remove specific incrustations.

Restoration Emergencies

The flood in Florence, Italy, in Nov., 1966, was among the greatest disasters in modern history in terms of the destruction of works of art. Conservators and restorers from all over the world applied emergency treatment to the treasures of painting, sculpture, and architecture that could be saved. Among those were five panels from the bronze doors of the Baptistery by Ghiberti, which had been ripped apart and ruined by the furious, oily waters. In replacing them experts made use of an exact replica of the doors in San Francisco. In 1972, Michelangelo's Pietá in St. Peter's, Rome, was attacked and mutilated by a madman with a hammer. The most delicate restoration work was required to make unobtrusive repairs on this masterpiece of sculpture. A number of well-known paintings also have been damaged by attackers in recent years, and these, too, have been restored as unobtrusively as possible. In a more recent emergency, a 1997 earthquake centered in the Italian town of Assisi damaged many works of art, most notably its 13th-cent. basilica. An international team worked on restoring its architectural and sculptural elements as well as its fragile frescoes. In late 1999 the newly earthquake-proofed and nearly completely restored basilica was reopened to the public; Giotto frescoes on two ceiling vaults still await restoration.

In physics, the principle that certain quantities within an isolated system do not change over time. When a substance in an isolated system changes phase, the total amount of mass does not change. When energy is changed from one form to another in an isolated system, there is no change in the total amount of energy. When a transfer of momentum occurs in an isolated system, the total amount of momentum is conserved. The same is true for electric charge in a system: charge lost by one particle is gained by another. Conservation laws make it possible to predict the macroscopic behaviour of a system without having to consider the microscopic details of a physical process or chemical reaction.

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Principle of physics according to which the energy of interacting bodies or particles in a closed system remains constant, though it may take different forms (e.g., kinetic energy, potential energy, thermal energy, energy in an electric current, or energy stored in an electric field, in a magnetic field, or in chemical bonds [see bonding]). With the advent of relativity physics in 1905, mass was recognized as equivalent to energy. When accounting for a system of high-speed particles whose mass increases as a consequence of their speed, the laws of conservation of energy and conservation of mass become one conservation law. Seealso Hermann von Helmholtz.

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Product of the mass of a particle and its velocity. Newton's second law of motion states that the rate of change of momentum is proportional to the force acting on the particle. Albert Einstein showed that the mass of a particle increases as its velocity approaches the speed of light. At the speeds treated in classical mechanics, the effect of speed on the mass can be neglected, and changes in momentum are the result of changes in velocity alone. If a constant force acts on a particle for a given time, the product of the force and the time interval, the impulse, is equal to the change in momentum. For any array of several objects, the total momentum is the sum of the individual momenta. Seealso angular momentum.

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Property that describes the rotary inertia of a system in motion about an axis. It is a vector quantity, having both magnitude and direction. The magnitude of the angular momentum of an object is the product of its linear momentum (mass math.m × velocity math.v) and the perpendicular distance math.r from the centre of rotation, or math.mmath.vmath.r. The direction is that of the axis of rotation. The angular momentum of an isolated system is constant. This means that a rigid spinning object continues to spin at a constant rate unless acted upon by an external torque. A spinning gyroscope in an airplane remains fixed in its orientation, independent of the airplane's motion, because of the conservation of direction as well as magnitude.

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Planned management of a natural resource or of a particular ecosystem to prevent exploitation, pollution, destruction, or neglect and to ensure the future usability of the resource. Living resources are renewable, minerals and fossil fuels are nonrenewable. In the West, conservation efforts date to 17th-century efforts to protect European forests in the face of increasing demands for fuel and building materials. National parks, first established in the 19th century, were dedicated to the preservation of uncultivated land not only to provide a safe haven to wildlife but to protect watershed areas and help ensure a clean water supply. National legislation and international treaties and regulations aim to strike a balance between the need for development and the need to conserve the environment for the future.

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Maintenance and preservation of works of art, their protection from future damage, deterioration, or neglect, and the repair or renovation of works that have deteriorated or been damaged. Research in art history has relied heavily on 20th- and 21st-century technical and scientific advances in art restoration. Modern conservation practice adheres to the principle of reversibility, which dictates that treatments should not cause permanent alteration to the object.

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(1933–42) U.S. unemployment program. One of the earliest New Deal programs, it was established to relieve unemployment during the Great Depression by providing national conservation work primarily for young unmarried men. Recruits lived in semimilitary work camps and received $30 a month as well as food and medical care. Projects included planting trees, building flood barriers, fighting forest fires, and maintaining forest roads and trails. It employed a total of 3 million men during its existence.

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