propeller Device with a central hub and radiating blades placed so that each forms part of a helical (spiral) surface, used to propel a vehicle such as a ship or airplane. By its rotation in water or air, the propeller produces thrust on the blades, which gives forward motion to the vehicle.
proper motion Apparent motion of a star across the celestial sphere at right angles to the observer’s line of sight, generally measured in seconds of arc per year. Any radial motion (toward or away from the observer) is not included. Edmond Halley was the first to detect proper motions; the largest known is that of Barnard's star, about 10 seconds yearly.
Propertius Xpro-'por-shos, pro-'por-she-asV, Sextus (b. 55/43, Assisi, Umbria—d. after 16 bc, Rome) Roman poet. Very few details of his life are known. The first and best known of his four books of elegies (see elegy), Cynthia, was published in 29 bc, the year he met its heroine (his mistress, whose real name was Hostia). She emerges from his poems as beautiful, uninhibited, jealous, and irresistible. In Book II his main theme is still love, but he also contemplates writing an epic, is preoccupied with thoughts of death, and attacks the materialism of his time. Books III and IV demonstrate a bold command of language and various literary forms; among the subjects are Roman mythology and history.
property In law, something that is owned or possessed. Concepts of property vary widely among cultures. In the West, property is generally regarded as either tangible (e.g., land or goods) or intangible (e.g., stocks and bonds or a patent). Individual ownership of property is emphasized in Western societies, whereas in many non-Western societies property own¬ ership is deemphasized or conceived on a more strictly communal basis. The use of property is extensively regulated throughout the West. Land- owners injured by adjoining land uses may sue in nuisance in Anglo- American countries; similar actions exist in civil-law countries. Throughout the West, landowners may agree to allow others to use their land in ways that would otherwise be actionable, and such agreements may be made to bind those to whom the land is conveyed. Anglo-American law tends to divide these grants of use rights into categories that reflect their common- law origins: easements (such as rights of way), profits (such as the right to take minerals or timber), real covenants (such as a promise to pay a home- owners’ association fee), and equitable servitudes (such as a promise to use the property for residential purposes only). The civil law has fewer catego¬ ries, the general category “servitudes” tending to cover for them all, and is a bit more restrictive. A common means of acquiring property is by transfer from the previous owner or owners. Such transfers include sales, dona¬ tions, and inheritance. See also adverse possession; community property; intel¬ lectual property; prescription; real and personal property.
property tax Levy imposed on real estate (land and buildings) and in some jurisdictions on personal property such as automobiles, jewelry, and
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furniture. Some countries also levy property taxes on farm equipment, business equipment, and inventories as well as intangibles such as stocks and bonds. Property taxes are usually levied by local or state governments rather than national governments, and they are a major source of tax rev¬ enue. Property taxes existed in the ancient world first as land taxes and later as taxes on farmhouses, livestock, and so on. The administration of a property tax involves identifying the property to be taxed, assessing its value, determining the appropriate tax rate, and collecting the requisite sum of money. Though sometimes burdensome to the poor, property taxes generally tend to redistribute the benefits of wealth from higher to lower income groups, since they often pay for schools and other services used by low-income groups. See also capital-gains tax; consumption tax; income tax; progressive tax; regressive tax.
prophet Person who speaks by divine inspiration, revealing or inter¬ preting the will of a god. Prophets have appeared in many religions throughout history. The most familiar in the West are such Old Testament leaders as Moses, Isaiah, and Daniel, along with the Prophet Muhammad. In contrast to the diviner or interpreter of omens (see divination), who may answer private questions, prophets often address the destiny and moral life of a whole people. Some prophets seek to create a new society that will realize their message and thus found new religions. Others may look only to reform or purify an existing society and religion. The tone of prophecy ranges widely, from ecstasy, inspired utterance, and ethical fer¬ vor to passionate social criticism, prediction of the future, and expecta¬ tion Of APOCALYPSE.
Prophet, The orig. Tenskwatawa (b. c. March 1768, Old Chilli- cothe, Ohio—d. 1834, Argentine, Kan., U.S.) North American Indian leader. The brother of Tecumseh, he maintained a strong following among the Shawnee on the strength of his 1805 declaration that he had received a message from the “Master of Life” and had contact with the supernatu¬ ral. Advocating a return to traditional ways of life, he rejected the white man’s introduction of alcohol, textile clothing, and individual ownership of property, and he worked with Tecumseh for an Indian confederacy to resist U.S. encroachment on Indian land. In Tecumseh’s absence he allowed the Shawnee to be drawn into and defeated at the Battle of Tippe¬ canoe (1811).
Prophet's Mosque House of worship built on the site of Muhammad’s house in Medina, considered one of the three holiest places of Islam. It was originally a simple brick structure surrounding an enclosed courtyard where people gathered to hear Muhammad. Muhammad later built roofed galleries to shelter his visitors, and in 628 a pulpit was added to raise him above the crowd. In 706 Caliph al-Walld I pulled down the original build¬ ing and built a mosque on the site, which contains Muhammad’s tomb. The mosque served as the model for later Islamic architecture.
proportion/proportionality In algebra, equality between two _ RATIOS. In the expression alb = dd, a and b are in the same proportion as
c and d. A proportion is typically set up to solve a word problem in which wm one of its four quantities is unknown. It is solved by multiplying one
M numerator by the opposite denominator and equating the product to that
of the other numerator and denominator. The term proportionality describes any relationship that is always in the same ratio. The number [jj| of apples in a crop, for example, is proportional to the number of trees in
the orchard, the ratio of proportionality being the average number of apples per tree.
proportional representation Electoral system in which the share of seats held by a political party in the legislature closely matches the share of popular votes it received. It was devised in Europe in the mid-19th century to guarantee minority groups more representation than was pos¬ sible under the majority or plurality systems. Its supporters claim that it cre¬ ates a more accurate reflection of public opinion; its opponents argue that by allowing more parties in a legislature, it may result in weaker, less stable governments. Two methods for apportioning seats are the single- transferable-vote method, under which voters rank candidates by prefer¬ ence, and the list system, under which voters select a party’s list of candidates rather than individuals. Some countries (e.g., Germany and Russia) use a combination of plurality and proportional methods for allo¬ cating seats in the lower house of the national legislature. See also leg¬ islative APPORTIONMENT.