Indra In the ancient Vedic religion of India, chief of the gods and patron of warriors. Armed with lightning and thunderbolts and strengthened by drinking the elixir soma, he vanquished demonic enemies and killed the dragon that kept the monsoon rains from breaking. In later Hinduism Indra was demoted to a rain god and regent of the heavens. He was father to Arjuna, hero of the A^ahabharata. Indra also appears in Buddhist and Jain mythologies.
Indre River Va n dr 3 \ River, central France. It is a tributary of the Loire River. Rising on the northern flanks of the plateau region known as the Massif Central, it flows northwest through agricultural lands and joins the Loire after a total course of 165 mi (265 km).
inductance Property of a conductor, sometimes in the shape of a coil, that is measured by the size of the electromotive force (emf), or voltage, induced in it, compared with the rate of change of the electric current that produces the voltage. A steadily changing electric current produces a varying magnetic field, which induces an emf in a conductor that is present in the field. The magnitude of this voltage is proportional to the rate of change of the current. The inductance is the proportionality factor. The unit of inductance is the henry, named after Joseph Henry; one henry is equivalent to one volt divided by one ampere per second.
induction In logic, a type of nonvalid inference or argument in which the premises provide some reason for believing that the conclusion is true. Typical forms of inductive argument include reasoning from a part to a whole, from the particular to the general, and from a sample to an entire population. Induction is traditionally contrasted with deduction. Many of the problems of inductive logic, including what is known as the problem of induction, have been treated in studies of the methodology of the natu¬ ral sciences. See also John Stuart Mill; philosophy of science; scientific
METHOD.
induction See electromagnetic induction, electrostatic induction
induction, problem of Problem of justifying the inductive inference from the observed to the unobserved. It was given its classic formulation by David Hume, who noted that such inferences typically rely on the assumption that the future will resemble the past, or on the assumption that events of a certain type are necessarily connected, via a relation of causation, to events of another type. (1) If we were asked why we believe that the sun will rise tomorrow, we would say that in the past the Earth turned on its axis every 24 hours (more or less), and that there is a uni¬ formity in nature that guarantees that such events always happen in the same way. But how do we know that nature is uniform in this sense? We might answer that, in the past, nature has always exhibited this kind of uniformity, and so it will continue to be uniform in the future. But this
© 2006 Encyclopaedia Britannica, Inc.
938 I induction Heating ► Indus River
PHILIPPINES
Banda Acehr-x,
Mounts MALAYSIA
Leuser 0 1/ i
n,090ft. \ K "Medan ®> Nuaia
% c
^ X Lumpur
% _% SINGAPORE
Padang
1
<h
501/77/
C7ffiV4 5E4
Bandar Seri BRUNEL®B a gawan 0 / v
MAI AVCIrt
X
ra ° a " S * SUMATRA
PACIFIC OCEAN
Mount Awu ^4,330 ft.
Manado .
HALMAHERA
ISLAND
Equator
•palembang tf/>
•11/,,, U '“"3 Pa " da "9
Jakarta ®. Semarang ° A
Baridung *
• ^
** .Palu ^Qj
su^wEX 5 X t/c %’ < "X" Vxv(S' apura
U r f xS»Kendari t ^b(Jn*''~^b > Lnmb in™
1 ,S UMDs
-java .Sarabaya EAST TIMOR
Kupang. TIM0R
BALI
BANDA SEA
' 0 P
INDIAN
OCEAN
SSER Si >NDA ISLANDS
Australia
ARAFURA
SEA
y
PAPUA f E V NEW
GUINEA GUINEA
D 2002 Encyclopaedia Britannica, Inc.
inference is justified only if we assume that the future must resemble the past. How do we justify this assumption? We might say that in the past, the future turned out to resemble the past, and so in the future, the future will again turn out to resemble the past. The inference is obviously circular: it succeeds only by tacitly assuming what it sets out to prove, namely that the future will resemble the past. (2) If we are asked why we believe we will feel heat when we approach a fire, we would say that fire causes heat—i.e., there is a “necessary connection” between fire and heat, such that whenever one occurs, the other must follow. But, Hume asks, what is this “neces¬ sary connection”? Do we observe it when we see the fire or feel the heat? If not, what evidence do we have that it exists? All we have is our obser¬ vation, in the past, of a “constant conjunction” of instances of fire being followed by instances of heat. This observation does not show that, in the future, instances of fire will continue to be followed by instances of heat; to say that it does is to assume that the future must resemble the past. But if our observation is consistent with the possibility that fire may not be followed by heat in the future, then it cannot show that there is a neces¬ sary connection between the two that makes heat follow fire whenever fire occurs. Thus we are not justified in believing that (1) the sun will rise tomorrow or that (2) we will feel heat when we approach a fire. It is important to note that Hume did not deny that he or anyone else formed beliefs about the future on the basis of induction; he denied only that we could know with certainty that these beliefs are true. Philosophers have responded to the problem of induction in a variety of ways, though none has gained wide acceptance.
induction heating Method of raising the temperature of an electri¬ cally conductive material by subjecting it to an alternating electromagnetic field. Energy in the electric currents induced in the object is dissipated as heat. Induction heating is used in metalworking to heat metals for solder¬ ing, tempering, and annealing, and in induction furnaces for melting and processing metals. The principle of the induction-heating process resembles that of the transformer. A water-cooled coil (inductor), acting as the primary winding of a transformer, surrounds the material to be heated (the workpiece), which acts as the secondary winding. Alternating current flowing in the primary coil induces eddy currents in the work- piece, causing it to become heated. The depth to which the eddy currents penetrate, and therefore the distribution of heat within the object, depend
on the frequency of the primary alternating current and the magnetic per¬ meability, as well as the resistivity, of the material.
indulgence In Roman Catholicism, the remission of temporal punish¬ ment for a sin after the sin has been forgiven through the sacrament of penance. The theology of indulgences is based on the concept that, even though the sin and its eternal punishment are forgiven through penance, divine justice demands that the sinner pay for the crime either in this life or in purgatory. The first indulgences were intended to shorten times of penance by substituting periods of fasting, private prayers, almsgiving, and monetary payments that were to be used for religious purposes. Pope Urban II granted the first plenary, or absolute, indulgence to participants in the First Crusade, and subsequent popes offered indulgences on the occasion of the later Crusades. After the 12th century they were more widely used, and abuses became common as indulgences were put up for sale to earn money for the church or to enrich unscrupulous clerics. Jan Hus opposed them, and Martin Luther’s Ninety-five Theses (1517) were in part a protest against indulgences. In 1562 the Council of Trent put an end to the abuses but not to the doctrine itself.
Indus civilization (c. 2500-c. 1700 bc) Earliest known urban culture of the Indian subcontinent and the most extensive of the world’s three earliest civilizations. It stretched from near the present-day Iran-Pakistan border on the Arabian Sea in the west to near Delhi in the east, and 500 mi (800 km) to the south and 1,000 mi (1,600 km) to the northeast. It is known to have included two large cities, Harappa and Mohenjo Daro (in what is now Pakistan), whose large size suggests centralization in two large states or one state with two capitals. Alternatively, Harappa may have succeeded Mohenjo Daro. It was a literate civilization; the language has been tentatively identified as Dravidian. Wheat and barley were grown, many animals (including cats, dogs, and cattle) were domesticated, and cotton was cultivated. The best-known artifacts are seals depicting real and imaginary animals. How and when the civilization came to an end is unclear; Mohenjo Daro was attacked and destroyed in the mid-2nd millennium bc, but in the south there was continuity between the Indus civilization and the Copper Age civilizations of central and western India.