Electrostatics is the study of the behavior of electric charges that are at rest. The phenomenon of static electricity has been known for well over 2,000 years, and a variety of electrostatic devices have been created over the centuries. In the late sixteenth century, William Gilbert (1544-1603) began experimenting with static electricity, pointing out the difference between static electric attrac…
A chemical element is a substance made up of only one kind of atom (atoms having the same atomic number). A compound, on the other hand, is made up of two or more kinds of atom combined together in specific proportions. The atomic number of an element is the number of protons found in the nucleus of each atom of that element; the number of protons in the nucleus equals the number of electrons that…
A family of chemical elements usually consists of elements that are in the same group (the same column) on the periodic table. The term is also applied to certain closely related elements within the same period (row). Just as the individual members in a human family are all different but have common characteristics, like hair color, so to do the elements in a chemical family have certain propertie…
A transuranium (beyond uranium) element is any of the chemical elements with atomic numbers higher than 92, which is the atomic number of uranium. Ever since the eighteenth century when chemists began to recognize certain substances as chemical elements, uranium had been the element with the highest atomic weight; it had the heaviest atoms of all the elements that could be found on Earth. The gene…
Elements are identified by the nuclei of the atoms of which they are made. For example, an atom having six protons in its nucleus is carbon, and one having 26 protons is iron. There are over 80 naturally occurring elements, with uranium (92 protons) being the heaviest (heavier nuclei have been produced in reactors on Earth). Nuclei also contain certain neutrons, usually in numbers greater than the…
Elephants are large, four-legged, herbivorous mammals. They have a tough, almost hairless hide, a long flexible trunk, and two ivory tusks growing from their upper jaw. Only two species of elephant exist today, the African elephant (Loxodonta africana) and the Asian or Indian elephant (Elephas maximus), both of which are threatened or endangered. African elephants are the largest of all land anima…
Elephant shrews are relatively small mammals in the family Macroscelididae, order Macroscelidea. Elephant shrews have a characteristic long, narrow snout that is broad at the base, and very sensitive and flexible but not retractile. This snout is movable in circular manner at the base, and has nostrils at the end. There are five genera with some 185 species of elephant shrews, living in continenta…
Elephant snout fish belong to a diverse group of fishes that comprise the family Mormyridae. All are freshwater species that are confined to tropical parts of the African continent. Some 150 species have been described so far. The group takes its common or English name from the animals' extended snout. This adaptation is taken to the extreme in the genus Gnathonemus which has a pendulous, t…
Elephantiasis is an extreme symptom of human infection by a type of roundworm or nematode. It involves massive swelling of a limb or of the scrotum. The leg of an individual suffering from elephantiasis can become enlarged to two or three times normal diameter. The actual name of the disease or infection which causes elephantiasis is lymphatic filariasis. Lymphatic filariasis is an important paras…
Elms are trees (occasionally shrubs) of flowering plants in the genus Ulmus. Elm leaves possess stipules, and often have a nonsymmetrical leaf, that is, one half is larger than the other so that the bottom ends do not meet where they are attached to the mid-rib. Elms flower in the spring. Their flowers lack petals, form reddish brown clusters in the tops of the trees, appear before the leaves have…
Embiids are small, cylindrical, soft-bodied insects in the order Embioptera that spin tubular galleries of silk, an ability that gives them the common name web-spinners. They have chewing mouthparts, and undergo paurometabolism, or gradual metamorphosis, exhibiting a definite egg, nymph, and adult stage. In the phylogeny, or evolutionary history of the class Insecta, embiids are thought to be most…
An embolism is the sudden blockage of a blood vessel by a blood clot that has been brought to that location by the bloodstream. The clot, called an embolus, from the Greek word meaning plug, is a blood clot that has formed inside the circulatory system and is floating in the bloodstream. It will remain on the move until it encounters a blood vessel too small for it to fit through, where it will pl…
An embryo is a stage directly after fertilization that signifies the early stages of growth and development of an organism. In humans, this stage ends during the third month of pregnancy, and is then called a fetus. Plants and invertebrate as well as vertebrate animals have an embryonic stage of development. For example, the embryo of the common North American leopard frog, Rana pipiens is from a …
Developments in reproductive technology are occurring at a rapid rate in animal science as well as in human biology. In vitro fertilization, embryo culture, preservation of embryos by freezing (cryopreservation), and cloning technology yield embryos that are produced outside of the female reproductive system. Embryo transfer permits continued survival of embryos by insertion into the female reprod…
Embryology is the study of the development of organisms. This is as true of plants as it is of animals. Seed formation proceeds following fertilization in higher plants. The seed consists of the embryo, the seed coat, and another part sometimes called the endosperm. While plants are extraordinarily important for survival of animal life, animal embryology is described here. The dictionary definitio…
In the context of ecology and environmental science, the word emission generally refers to a release of a A nickel smelting facility emitting pollutants that carry for hundreds of miles in Russian Siberia. Photograph by Josef Polleross. Stock Market. Reproduced by permission. substance or energy to the environment. Often, emissions refer to substances or energy that are ecological stresso…
Ideas about emotions and their function in human and animal life have been a major theme in philosophy—and more recently in psychology and the social sciences—since the time of the ancient Greeks. The history of ideas about emotion is an essential part of the history of ideas about human nature and about human continuity—and discontinuity—with other animals. Whether emo…
Emphysema is an incurable lung disease that results in the destruction of air sacs in the lungs. It is brought about almost exclusively by smoking. In the past, the majority of its victims were male, but the disease has become more common in women as more women smoke. Emphysema is also called chronic obstructive pulmonary (or lung) disease (COPD or COLD). Chronic bronchitis, that is, inflammation …
An empire presupposes an unequal relationship between an elite of an ethnicity, or polity and the peoples of a dependent and subservient ethnicity or polity, the periphery, on issues such as service or tribute and dominant language and culture, as shown by unequal material or service exchanges and the spread of art styles, architectural forms, and politico-religious practices. The Americas have a …
While this was going on, the rest of the Asian landmass to the Urals and the Caucasus was dominated by four other powerful and expanding empires: Mughal India in the south, Safavid Iran in the southwest, Ottoman Turkey and the Middle East in the west, and Romanov Russia in the central region and the north. The last was led by Russian-speaking Slavs from northeastern Europe, but the other three sha…
Few subjects have generated as much controversy as that of European imperialism in the nineteenth and twentieth centuries. Because of the term's pejorative connotations, even attempting to define it causes difficulties. What, precisely, constitutes an empire? Is any relationship between two societies involving an imbalance of power in some way "imperial"? For many years, imper…
The question of whether the United States is an imperial power that, like other previous imperial powers, has been acquiring an empire of its own has been hotly contested in U.S. political history. On the one hand, the United States likes to think of itself as different from other powers in the past who have acquired empires, because its motives are supposedly superior (democracy, human rights, a…
Empiricism is a family of theories of knowledge (epistemology) claiming that all knowledge about the extant universe is based on experience, primarily on perception via the five senses. Some empiricists add introspection, a moral sense, or a special sensitivity to religious or aesthetic experience. Strong empiricists claim that all knowledge whatever derives from experience. They must show how emp…
Encephalitis is an inflammatory disease of the brain. It is caused by a virus that either has invaded the brain, or a virus encountered elsewhere in the body that has caused a sensitivity reaction in the brain. Most cases of encephalitis are considered secondary to a virus infection that stimulates an immune reaction. An infection that involves the membranes associated with the spinal cord is call…
An endangered species of plant, animal, or microorganism is at risk of imminent extinction or extirpation in all or most of its range. Extinct species no longer occur anywhere on Earth, and once gone they are gone forever. Extirpated species have disappeared locally or regionally, but still survive in other regions or in captivity. Threatened species are at risk of becoming endangered in the fores…
Endemic is a biogeographic term referring to a distinct race or species that originated in a local place or region, and that has a geographically restricted distribution. Endemic species tend to occur in certain ecological contexts, being especially frequent in places that are ecologically isolated, and that have not been affected by a regional-scale, catastrophic disturbance for a very long time.…
The endocrine system is the body's network of nine glands and over 100 hormones which maintain and regulate numerous events throughout the body. The glands of the endocrine system include the pituitary, thyroid, parathyroids, thymus, pancreas, pineal, adrenals, and ovaries or testes: in addition, the hypothalamus, in the brain, regulates the release of pituitary hormones. Each of these glan…
The phylum Endoprocta is a group of about 60 species that closely resemble moss animals or members of the phylum Bryozoa. With the exception of the genus Urnatella all endoprocts are marine-dwelling species. Like moss animals they are sessile, being attached to a wide range of submerged objects such as rocks, shells, sponges, corals, and other objects. These tiny animals—the largest measure…
Endoscopy is the use of a thin, lengthy, flexible scope that can be inserted into the body for the diagnosis and treatment of various conditions. Until the last third of the twentieth century, one of the limiting factors in the treatment of internal injuries or diseases was the need to perform open surgery on the patient. That meant putting him under anesthesia, carrying out the operation, sewing …
The term endothermic has two distinct meanings, depending on the context in which it is used. In chemistry, endothermic means that a chemical reaction or phase transition absorbs heat. (A phase transition is the transformation of matter from a gas, liquid, or solid into a different one of these states.) In physiology, the term endothermic refers to organisms which metabolically generate heat to ma…
Energy is a state function commonly defined as the capacity to do work. Since work is defined as the movement of an object through a distance, energy can also be described as the ability to move an object through a distance. As an example, imagine that a bar magnet is placed next to a pile of iron filings (thin slivers of iron metal). The iron filings begin to move toward the iron bar because magn…
An energy budget describes the ways in which energy is transformed from one state to another within some defined system, including an analysis of inputs, outputs, and changes in the quantities stored. Ecological energy budgets focus on the use and transformations of energy in the biosphere or its components. Solar electromagnetic radiation is the major input of energy to Earth. This external sourc…
Energy transfer describes the changes in energy (a state function) that occur between organisms within an ecosystem. Living organisms are constantly changing as they grow, move, reproduce, and repair tissues. These changes are fueled by energy. Plants, through photosynthesis, capture some of the Sun's radiant energy and transform it into chemical energy, which is stored as plant biomass. Th…
Engraving and etching are processes used to make intaglio prints. An intaglio print is made from a plate, usually a metal one, which has been had lines drawn into its surface. These lines trap ink when the ink is rolled across the surface of the plate. When the surface of the plate is wiped with a cloth, the lines retain their ink. A piece of damp paper is placed on the plate, and the two are run …
In the years since the publication of the first Dictionary of the History of Ideas, the Enlightenment has become an increasingly fragmented and decreasingly coherent historical rubric. In fact that fragmentation began in the Dictionary of the History of Ideas itself, in an article titled "Counter-Enlightenment," written by Isaiah Berlin and categorized out of alphabetical order, appe…
Enterobacteria are bacteria from the family Enterobacteriaceae, which are primarily known for their ability to cause intestinal upset. Enterobacteria are responsible for a variety of human illnesses, including urinary tract infections, wound infections, gastroenteritis, meningitis, septicemia, and pneumonia. Some are true intestinal pathogens; whereas others are merely opportunistic pests which at…
Entropy is a physical quantity that is primarily a measure of the thermodynamic disorder of a physical system. Entropy has the unique property in that its global value must always increase or stay the same; this property is reflected in the second law of thermodynamics. The fact that entropy must always increase in natural processes introduces the concept of irreversibility, and defines a unique d…
The term environment became specialized beginning in about the 1960s to designate the context of human and animal groups, with a special emphasis on the natural world and its physical and vegetal components. Within this framework, the word took on an even more limited meaning and in the early twenty-first century refers primarily to the interaction between human and animal activity on the one hand…
Ethics is a branch of philosophy that primarily discusses issues dealing with human behavior and character. Ethics attempts to establish a basis for judging right from wrong and good from bad. Environmental ethics employs concepts from the entire field of philosophy, especially aesthetics, metaphysics, epistemology, philosophy of science, and social and political philosophy in an effort to relate …
Environmental history is the study of the changing affairs of humans within the natural world. This definition, in contrast to other useful phrasings, such as the study of "interactions between humans and nature" (Merchant, 2002, p. xv), embodies a fundamental, not merely semantic, point of emphasis. First, and obviously, humans are part of nature, biological organisms subject to the…
In the United States, the National Environmental Policy Act (NEPA) requires federal agencies to file an Environmental Impact Statement (EIS) for any major project or legislative proposal that may have significant environmental effects. According to the U.S. Environmental Protection Agency (EPA), "NEPA requires federal agencies to integrate environmental values into their decision making pro…
The introduction of the techniques of modern molecular biology, beginning in the 1970s, have made possible the genetic engineering of proteins. New proteins can be created and existing proteins altered. Enzymes are proteins that function in chemical reactions by making the reaction occur more easily than if the enzyme was absent. Enzymatic engineering includes a wide variety of techniques related …