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Philogiston Theory

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Phlogiston Theory

According to the phlogiston theory, propounded in the 17th century, every combustible substance consisted of a hypothetical principle of fire known as phlogiston,

which was liberated through burning, and a residue. The word phlogiston was first used early in the 18th century by the German chemist Georg Ernst Stahl. Stahl

declared that the rusting of iron was also a form of burning in which phlogiston was freed and the metal reduced to an ash or calx. The theory was superseded

between 1770 and 1790 when the French chemist Antoine Lavoisier showed that burning and rusting both involved oxygen and concluded that both ash and rust

were compounds of oxygen. Lavoisier's oxidization theory has been accepted by scientists from about 1800 to the present day.

The theory of phlogiston was predominantly German in origin, with much early work done in Mainz, though it was widely believed through much of the eighteenth

century -- two of the most prominent followers of the theory, Johann Joachim Becher and Georg Ernst Stahl (who first used the name phlogiston in 1700), were

Swedish. Phlogiston was not only widespread but deep-seated, and gave way to the atomic theory only slowly.

Phlogiston theorists identified three essences which comprise all matter: sulfur or terra pinguis, the essence of inflammability; mercury or terra mercurialis, the

essence of fluidity; and salt or terra lapida, the essence of fixity and inertness. In this respect phlogiston theory is similar to the ancient alchemical notions of earth,

air, fire, and water. The terra pinguis was renamed phlogiston. In this view, metals were made of a "calx" (or residue) combined with phlogiston, the fiery principle,

which was liberated during combustion, leaving only the calx. Air, according to the theory, was merely the receptacle for phlogiston; all combustible or calcinable

substances, in fact, were not elements but compounds containing phlogiston. Rusting iron, for instance, was believed to be losing its phlogiston and thereby returning

to its elemental state.

Phlogiston theory was widely supported throughout the eighteenth century, although it came under increasing attack as empirical research pointed up its difficulties.

When it was determined that some metals actually gained mass when burnt, partisans explained it by giving phlogiston a negative mass. Even Priestley believed in the

theory until his death, convinced that his discovery of oxygen was "dephlogisticated air." It was up to Lavoisier to realize the significance of his discovery.

Lavoisier made a symbolic break with phlogiston theory by burning all textbooks that supported the theory, just as Paracelsus had destroyed his copies of the works

of the medieval medical authorities. His theory of oxidation soon replaced phlogiston theory, and remains a part of modern chemistry.

Although he exaggerated its importance, Lavoisier was the first to understand the significance of

Priestley's work on oxygen, and is considered by some to have discovered the element. He

disproved phlogiston theory by demonstrating that oxygen is required for combustion, rusting, and

respiration. He combined his chemical abilities with an interest in zoology to produce pioneering

work on anatomy and physiology.

phlogiston theory , hypothesis regarding combustion. The theory,

advanced by J. J. Becher late in the 17th cent. and extended and

popularized by G. E. Stahl, postulates that in all flammable materials there is

present phlogiston, a substance without color, odor, taste, or weight that is

given off in burning. APhlogisticated@ substances are those that contain

phlogiston and, on being burned, are Adephlogisticated.@ The ash of the

burned material is held to be the true material. The theory received strong

and wide support throughout a large part of the 18th cent. until it was

refuted by the work of A. L. Lavoisier, who revealed the true nature of

combustion. Joseph Priestley, however, defended the theory throughout his

lifetime. Henry Cavendish remained doubtful, but most other chemists of the

period, including C. L. Berthollet, rejected it.

Phlogiston Theory

The failure to understand combustion was an insurmountable obstacle to real progress in

chemistry. Any theory of chemical change must be able to explain combustion and phlogiston

was the first real attempt to do so.

The fact that wood turns to ashes and metals become soft powders when heated and can be

changed back into metals in the presence of charcoal is hard to reconcile without imagining the

addition or subtraction of some substance.

Phlogiston was that substance.

The theory was simple, and although having serious contradictions, was better than no theory at

all. Besides, despite the quantitative work of Galileo and Newton, the importance of quantitative

measurements had not yet been impressed upon the chemists.

The phlogiston theory was really quite simple.

Metals and combustible substances contained an imponderable substance known as phlogiston

which was released into the air along with caloric. Air had a limited capacity to absorb

phlogiston.

Since phlogiston was an imponderable substance, itХs properties were incapable of being

detected by senses and could be contradictory.

Sometimes it had weight, sometimes it had negative weight, and sometimes it had no weight at

all.

Phlogiston theory explained many facts about combustion

1.combustibles lose weight when burning because they lose phlogiston

2.a flame goes out in an enclosed space because air becomes saturated with phlogiston

3.charcoal leaves little residue upon burning because it is nearly pure phlogiston

4.a mouse dies in an airtight space because the air becomes saturated with phlogiston

5.some metal calxes turn to metals when heated with charcoal because phlogiston from

charcoal is restored to the calx

A serious problem was that the calx formed when a metal such as magnesium burns weighs more

than the metal from which it formed, just as a rusty nail weighs more than the nail.

The supporters of the phlogiston theory answered this by postulating that metallic phlogiston has

negative weight while other combustibles contain phlogiston with positive weight.

Adding a special postulate such as this signaled a theory in trouble and led to the ultimate

demise of the theory.

phlogiston theory

phlogiston theory

Pronounced As: flojiston , hypothesis regarding

combustion. The theory, advanced by J. J. Becher late

in the 17th cent. and extended and popularized by G. E.

Stahl, postulates that in all flammable materials there

is present phlogiston, a substance without color, odor,

taste, or weight that is given off in burning.

"Phlogisticated substances are those that contain

phlogiston and, on being burned, are

"dephlogisticated. The ash of the burned material is

held to be the true material. The theory received strong

and wide support throughout a large part of the 18th

cent. until it was refuted by the work of A. L. Lavoisier,

who revealed the true nature of combustion. Joseph

Priestley, however, defended the theory throughout his

lifetime. Henry Cavendish remained doubtful, but most

other chemists of the period, including C. L. Berthollet,

rejected it.

Hippocrates of Cos (460-ca. 370 BC)

Greek physician who founded a medical school on Cos. This school produced more than 50

books, as well a system of medical methodology and ethics which is still practiced today. Upon

being granted their M. D. degrees, new doctors still swear a so-called Hippocratic oath. In On

Ancient Medicine, Hippocrates stated that medicine is not philosophy, and therefore must be

practiced on a case-by-case basis rather than from first principles. In The Sacred Disease, he

stated that epilepsy (and disease in general) do not have divine causes. He advocated clinical

observations, diagnosis, and prognosis, and argued that specific diseases come from specific

causes. Hippocrates's methodology relied on physical examination of the patient and proceeded in

what was, for the most part, a highly rational deductive framework of understanding through

observation. (An exception was the belief that disease was caused by "isonomia", an imbalance in

the four humors originally suggested by Empedocles and consisting of yellow bile, blood, phlegm,

and black bile.) The Hippocratic corpus of knowledge was widely distributed, highly influential,

and marked the rise of rationality in both medicine and the physical sciences.

Galen of Pergamum (ca. 130-ca. 200)

Greek physician considered second only to Hippocrates of Cos in his importance to the

development of medicine, Galen performed extensive dissections and vivisections on animals.

Although human dissections had fallen into disrepute, he also performed and stressed to his

students the importance of human dissections. He recommended that students practice dissection

as often as possible. He studied the muscles, spinal cord, heart, urinary system, and proved that

the arteries are full of blood. He believed that blood originated in the liver, and sloshed back and

forth through the body, passing through the heart, where it was mixed with air, by pores in the

septum. Galen also introduced the spirit system, consisting of natural spirit or "pneuma" (air he

thought was found in the veins), vital spirit (blood mixed with air he believed to found in the

arteries), and animal spirit (which he believed to be found in the nervous system). In On the

Natural Facilities, Galen minutely described his experimentation on a living dog to investigate the

bladder and flow of urine. It was Galen who first introduced the notion of experimentation to

medicine.

Galen believed everything in nature has a purpose, and that nature uses a single object for more

than one purpose whenever possible. He maintained that "the best doctor is also a philosopher," and so advocated that medical students be well-versed in philosophy, logic, physics, and ethics. Galen and his work On the Natural Faculties remained the authority

on medicine until Vesalius in the sixteenth century, even though many of his views about human anatomy were false since he had performed his dissections on pigs, Barbary apes, and dogs. Galen mistakenly maintained, for instance, that humans have a five-lobed liver (which dogs do) and that the heart had only two chambers (it has four).

Erasistratus of Chios (ca. 304-ca. 250 BC)

Greek anatomist who continued the systematic investigation of anatomy begun by Herophilus in Alexandria. He described the cerebrum

and cerebellum, studied nerves (which he believed to be hollow) and the valves of the heart. He distinguished between veins and arteries, believing the latter to be full of air. He proposed mechanical explanations for many bodily processes, such as digestion. He believed in a tripartite system of humors consisting of nervous spirit (carried by nerves), animal spirit (carried by the arteries), and blood

(carried by the veins). After the work of Erasistratus, the use of dissection and study of anatomy declined.

Vesalius (1514-1564)

Flemish anatomist who founded the sixteenth century heritage of careful observation characterized

by "refinement of observation." Vesalius changed the organization of the medical school

classroom, bringing the students close to the operating table. He demonstrated that, in many

instances, Galen and Mondino de' Luzzi were incorrect (the heart, for instance, has four

chambers). He conducted his own dissections, and worked from the outside in so as not to

damage the cadaver while cutting into it. Vesalius also wrote the first anatomically accurate

medical textbook, De Humani Corporis Fabrica (1543), which was complete with precise

illustrations. Vesalius's careful observation, emphasis on the active participation of medical

students in dissection lectures, and anatomically accurate textbooks revolutionized the practice of

medicine. Through Vesalius's efforts, medicine was now on the road to its modern

implementation, although major modifications and leaps of understanding were, of course,

necessary to make its practice actually safe for the patient.

Harvey, William (1578-1657)

English physician who, by observing the action of the heart in small animals and fishes, proved that

heart receives and expels blood during each cycle. Experimentally, he also found valves in the

veins, and correctly identified them as restricting the flow of blood in one direction. He developed

the first complete theory of the circulation of blood, believing that it was pushed throughout the

body by the heart's contractions. He published his observations and interpretations in Exercitatio

Anatomica de Motu Cordis et Sanguinis in Animalibus (1628), often abbreviated De Motu

Cordis.

Harvey also noted, as earlier anatomists, that fetal circulation short circuits the lungs. He

demonstrated that this is because the lungs were collapsed and inactive. Harvey could not explain,

however, how blood passed from the arterial to the venous system. The discovery of the

connective capillaries would have to await the development of the microscope and the work of Malpighi. He was heavily influenced bythe mechanical philosophy in his investigations of the flow of blood through the body. In fact, he used a mechanical analogy withhydraulics. He could not, however, explain why the heart beats. Furthermore, Harvey used quantitative methods to measure the

capacity of the ventricles.

Harvey was the first doctor to use quantitative and observation methods simultaneously in his medical investigations. In Exercitationesde Generatione Animalium (On the Generation of Animals, 1651), he was extremely skeptical of spontaneous generation and proposed that all animals originally came from an egg. His experiments with chick embryos were the first to suggest the theory of

epigenesis, which views organic development as the production in a cumulative manner of increasingly complex structures from aninitially homogeneous material.

Lavoisier, Antoine (1743-1794)

French chemist who, through a conscious revolution, became the father of modern chemistry. As

a student, he stated "I am young and avid for glory." He was educated in a radical tradition, a

friend of Condillac and read Maquois's dictionary. He won a prize on lighting the streets of Paris,

and designed a new method for preparing saltpeter. He also married a young, beautiful

13-year-old girl named Marie-Anne, who translated from English for him and illustrated his

books. Lavoisier demonstrated with careful measurements that transmutation of water to earth

was not possible, but that the sediment observed from boiling water came from the container. He

burnt phosphorus and sulfur in air, and proved that the products weighed more than he original.

Nevertheless, the weight gained was lost from the air. Thus he established the Law of

Conservation of Mass.

Repeating the experiments of Priestley, he demonstrated that air is composed of two parts, one of

which combines with metals to form calxes. However, he tried to take credit for Priestley's

discovery. This tendency to use the results of others without acknowledgment then draw

conclusions was characteristic of Lavoisier. In Considйrations Gйnйrales sur la Nature des

Acides (1778), he demonstrated that the "air" responsible for combustion was also the source of

acidity. The next year, he named this portion oxygen (Greek for acid-former), and the other azote (Greek for no life). He also

discovered that the inflammable air of Cavendish which he termed hydrogen (Greek for water-former), combined with oxygen to

produce a dew, as Priestley had reported, which appeared to be water.

In Reflexions sur le Phlogistique (1783), Lavoisier showed the phlogiston theory to be inconsistent. In Methods of Chemical

Nomenclature (1787), he invented the system of chemical nomenclature still largely in use today, including names such as sulfuric acid,

sulfates, and sulfites. His Traitй Йlйmentaire de Chimie (Elementary Treatise of Chemistry, 1789) was the first modern chemical

textbook, and presented a unified view of new theories of chemistry, contained a clear statement of the Law of Conservation of Mass,

and denied the existence of phlogiston. In addition, it contained a list of elements, or substances that could not be broken down further,

which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulfur. His list, however, also included light, and caloric,

which he believed to be material substances. In the work, Lavoisier underscored the observational basis of his chemistry, stating "I

have tried...to arrive at the truth by linking up facts; to suppress as much as possible the use of reasoning, which is often an unreliable

instrument which deceives us, in order to follow as much as possible the torch of observation and of experiment." Nevertheless, he

believed that the real existence of atoms was philosophically impossible. Lavoisier demonstrated that organisms disassemble and

reconstitute atmospheric air in the same manner as a burning body.

With Laplace, he used a calorimeter to estimate the heat evolved per unit of carbon dioxide produced. They found the same ratio for a

flame and animals, indicating that animals produced energy by a type of combustion. Lavoisier believed in the radical theory, believing

that radicals, which function as a single group in a chemical reaction, would combine with oxygen in reactions. He believed all acids

contained oxygen. He also discovered that diamond is a crystalline form of carbon. Lavoisier made many fundamental contributions to

the science of chemistry. The revolution in chemistry which he brought about was a result of a conscious effort to fit all experiments into

the framework of a single theory. He established the consistent use of chemical balance, used oxygen to overthrow the phlogiston

theory, and developed a new system of chemical nomenclature. He was beheaded during the French revolution.

avoisier, Antoine Laurent

Pronounced As: дNtwдn lorдN lдvwдzya , 1743-94,

French chemist and physicist, a founder of modern

chemistry. He studied under eminent men of his day,

won early recognition, and was admitted to the

Academy of Sciences in 1768. Much of his work was

the result of extending and coordinating the research of

others; his concepts were largely evolved through his

superior ability to organize and interpret and were

substantiated by his own experiments. He was one of

the first to introduce effective quantitative methods in

the study of chemical reactions. He explained

combustion and thereby discredited the phlogiston

theory. He also described clearly the role of oxygen in

the respiration of both animals and plants. His

classification of substances is the basis of the modern

distinction between chemical elements and

compounds and of the system of chemical

nomenclature. He also conducted experiments to

establish the composition of water and of many

organic compounds. Lavoisier worked as well to

improve economic and social conditions in France,

holding various government posts. He was appointed

director of the gunpowder commission (1775),

member of the committee on agriculture (1785),

director of the Academy of Sciences (1785), member of

the commission on weights and measures (1790),

and commissioner of the treasury (1791). As one of the

farmers general, however, charged with the collection

of taxes, he was guillotined during the Reign of Terror.

His works include Traitй йlйmentaire de chimie (1789)

and the posthumously published Mйmoires de chimie

(1805).

Lavoisier, Antoine Laurent , 1743B94, French chemist and physicist, a

founder of modern chemistry. He studied under eminent men of his day, won

early recognition, and was admitted to the Academy of Sciences in 1768.

Much of his work was the result of extending and coordinating the research

of others; his concepts were largely evolved through his superior ability to

organize and interpret and were substantiated by his own experiments. He

was one of the first to introduce effective quantitative methods in the

study of chemical reactions. He explained combustion and thereby

discredited the phlogiston theory. He also described clearly the role of

oxygen in the respiration of both animals and plants. His classification of

substances is the basis of the modern distinction between chemical

elements and compounds and of the system of chemical nomenclature. He

also conducted experiments to establish the composition of water and of

many organic compounds. Lavoisier worked as well to improve economic and

social conditions in France, holding various government posts. He was

appointed director of the gunpowder commission (1775), member of the

committee on agriculture (1785), director of the Academy of Sciences

(1785), member of the commission on weights and measures (1790), and

commissioner of the treasury (1791). As one of the farmers general,

however, charged with the collection of taxes, he was guillotined during the

Reign of Terror. His works include Traitй йlйmentaire de chimie (1789) and

the posthumously published Mйmoires de chimie (1805).

Introduction to the Scientific Method

The scientific method is the process by which scientists, collectively and over time, endeavor to construct an accurate (that is,

reliable, consistent and non-arbitrary) representation of the world.

Recognizing that personal and cultural beliefs influence both our perceptions and our interpretations of natural phenomena, we aim

through the use of standard procedures and criteria to minimize those influences when developing a theory. As a famous scientist

once said, "Smart people (like smart lawyers) can come up with very good explanations for mistaken points of view." In summary,

the scientific method attempts to minimize the influence of bias or prejudice in the experimenter when testing an hypothesis or a

theory.

I. The scientific method has four steps

1. Observation and description of a phenomenon or group of phenomena.

2. Formulation of an hypothesis to explain the phenomena. In physics, the hypothesis often takes the form of a causal mechanism or

a mathematical relation.

3. Use of the hypothesis to predict the existence of other phenomena, or to predict quantitatively the results of new observations.

4. Performance of experimental tests of the predictions by several independent experimenters and properly performed experiments.

If the experiments bear out the hypothesis it may come to be regarded as a theory or law of nature (more on the concepts of

hypothesis, model, theory and law below). If the experiments do not bear out the hypothesis, it must be rejected or modified. What

is key in the description of the scientific method just given is the predictive power (the ability to get more out of the theory than you

put in; see Barrow, 1991) of the hypothesis or theory, as tested by experiment. It is often said in science that theories can never be

proved, only disproved. There is always the possibility that a new observation or a new experiment will conflict with a long-standing

theory.

II. Testing hypotheses

As just stated, experimental tests may lead either to the confirmation of the hypothesis, or to the ruling out of the hypothesis. The

scientific method requires that an hypothesis be ruled out or modified if its predictions are clearly and repeatedly incompatible with

experimental tests. Further, no matter how elegant a theory is, its predictions must agree with experimental results if we are to

believe that it is a valid description of nature. In physics, as in every experimental science, "experiment is supreme" and experimental

verification of hypothetical predictions is absolutely necessary. Experiments may test the theory directly (for example, the

observation of a new particle) or may test for consequences derived from the theory using mathematics and logic (the rate of a

radioactive decay process requiring the existence of the new particle). Note that the necessity of experiment also implies that a

theory must be testable. Theories which cannot be tested, because, for instance, they have no observable ramifications (such as, a

particle whose characteristics make it unobservable), do not qualify as scientific theories.

If the predictions of a long-standing theory are found to be in disagreement with new experimental results, the theory may be

discarded as a description of reality, but it may continue to be applicable within a limited range of measurable parameters. For

example, the laws of classical mechanics (Newton's Laws) are valid only when the velocities of interest are much smaller than the

speed of light (that is, in algebraic form, when v/c << 1). Since this is the domain of a large portion of human experience, the laws of

classical mechanics are widely, usefully and correctly applied in a large range of technological and scientific problems. Yet in nature

we observe a domain in which v/c is not small. The motions of objects in this domain, as well as motion in the "classical" domain, are

accurately described through the equations of Einstein's theory of relativity. We believe, due to experimental tests, that relativistic

theory provides a more general, and therefore more accurate, description of the principles governing our universe, than the earlier

"classical" theory. Further, we find that the relativistic equations reduce to the classical equations in the limit v/c << 1. Similarly,

classical physics is valid only at distances much larger than atomic scales (x >> 10-8 m). A description which is valid at all length

scales is given by the equations of quantum mechanics.

We are all familiar with theories which had to be discarded in the face of experimental evidence. In the field of astronomy, the

earth-centered description of the planetary orbits was overthrown by the Copernican system, in which the sun was placed at the

center of a series of concentric, circular planetary orbits. Later, this theory was modified, as measurements of the planets motions

were found to be compatible with elliptical, not circular, orbits, and still later planetary motion was found to be derivable from

Newton's laws.

Error in experiments have several sources. First, there is error intrinsic to instruments of measurement. Because this type of error has

equal probability of producing a measurement higher or lower numerically than the "true" value, it is called random error. Second,

there is non-random or systematic error, due to factors which bias the result in one direction. No measurement, and therefore no

experiment, can be perfectly precise. At the same time, in science we have standard ways of estimating and in some cases reducing

errors. Thus it is important to determine the accuracy of a particular measurement and, when stating quantitative results, to quote the

measurement error. A measurement without a quoted error is meaningless. The comparison between experiment and theory is made

within the context of experimental errors. Scientists ask, how many standard deviations are the results from the theoretical

prediction? Have all sources of systematic and random errors been properly estimated? This is discussed in more detail in the

appendix on Error Analysis and in Statistics Lab 1.

III. Common Mistakes in Applying the Scientific Method

As stated earlier, the scientific method attempts to minimize the influence of the scientist's bias on the outcome of an experiment.

That is, when testing an hypothesis or a theory, the scientist may have a preference for one outcome or another, and it is important

that this preference not bias the results or their interpretation. The most fundamental error is to mistake the hypothesis for an

explanation of a phenomenon, without performing experimental tests. Sometimes "common sense" and "logic" tempt us into believing

that no test is needed. There are numerous examples of this, dating from the Greek philosophers to the present day.

Another common mistake is to ignore or rule out data which do not support the hypothesis. Ideally, the experimenter is open to the

possibility that the hypothesis is correct or incorrect. Sometimes, however, a scientist may have a strong belief that the hypothesis is

true (or false), or feels internal or external pressure to get a specific result. In that case, there may be a psychological tendency to

find "something wrong", such as systematic effects, with data which do not support the scientist's expectations, while data which do

agree with those expectations may not be checked as carefully. The lesson is that all data must be handled in the same way.

Another common mistake arises from the failure to estimate quantitatively systematic errors (and all errors). There are many

examples of discoveries which were missed by experimenters whose data contained a new phenomenon, but who explained it away

as a systematic background. Conversely, there are many examples of alleged "new discoveries" which later proved to be due to

systematic errors not accounted for by the "discoverers."

In a field where there is active experimentation and open communication among members of the scientific community, the biases of

individuals or groups may cancel out, because experimental tests are repeated by different scientists who may have different biases.

In addition, different types of experimental setups have different sources of systematic errors. Over a period spanning a variety of

experimental tests (usually at least several years), a consensus develops in the community as to which experimental results have

stood the test of time.

IV. Hypotheses, Models, Theories and Laws

In physics and other science disciplines, the words "hypothesis," "model," "theory" and "law" have different connotations in relation

to the stage of acceptance or knowledge about a group of phenomena.

An hypothesis is a limited statement regarding cause and effect in specific situations; it also refers to our state of knowledge before

experimental work has been performed and perhaps even before new phenomena have been predicted. To take an example from

daily life, suppose you discover that your car will not start. You may say, "My car does not start because the battery is low." This is

your first hypothesis. You may then check whether the lights were left on, or if the engine makes a particular sound when you turn

the ignition key. You might actually check the voltage across the terminals of the battery. If you discover that the battery is not low,

you might attempt another hypothesis ("The starter is broken"; "This is really not my car.")

The word model is reserved for situations when it is known that the hypothesis has at least limited validity. A often-cited example of

this is the Bohr model of the atom, in which, in an analogy to the solar system, the electrons are described has moving in circular

orbits around the nucleus. This is not an accurate depiction of what an atom "looks like," but the model succeeds in mathematically

representing the energies (but not the correct angular momenta) of the quantum states of the electron in the simplest case, the

hydrogen atom. Another example is Hook's Law (which should be called Hook's principle, or Hook's model), which states that the

force exerted by a mass attached to a spring is proportional to the amount the spring is stretched. We know that this principle is only

valid for small amounts of stretching. The "law" fails when the spring is stretched beyond its elastic limit (it can break). This principle,

however, leads to the prediction of simple harmonic motion, and, as a model of the behavior of a spring, has been versatile in an

extremely broad range of applications.

A scientific theory or law represents an hypothesis, or a group of related hypotheses, which has been confirmed through repeated

experimental tests. Theories in physics are often formulated in terms of a few concepts and equations, which are identified with "laws

of nature," suggesting their universal applicability. Accepted scientific theories and laws become part of our understanding of the

universe and the basis for exploring less well-understood areas of knowledge. Theories are not easily discarded; new discoveries

are first assumed to fit into the existing theoretical framework. It is only when, after repeated experimental tests, the new

phenomenon cannot be accommodated that scientists seriously question the theory and attempt to modify it. The validity that we

attach to scientific theories as representing realities of the physical world is to be contrasted with the facile invalidation implied by the

expression, "It's only a theory." For example, it is unlikely that a person will step off a tall building on the assumption that they will

not fall, because "Gravity is only a theory."

Changes in scientific thought and theories occur, of course, sometimes revolutionizing our view of the world (Kuhn, 1962). Again,

the key force for change is the scientific method, and its emphasis on experiment.

V. Are there circumstances in which the Scientific Method is not applicable?

While the scientific method is necessary in developing scientific knowledge, it is also useful in everyday problem-solving. What do

you do when your telephone doesn't work? Is the problem in the hand set, the cabling inside your house, the hookup outside, or in

the workings of the phone company? The process you might go through to solve this problem could involve scientific thinking, and

the results might contradict your initial expectations.

Like any good scientist, you may question the range of situations (outside of science) in which the scientific method may be applied.

From what has been stated above, we determine that the scientific method works best in situations where one can isolate the

phenomenon of interest, by eliminating or accounting for extraneous factors, and where one can repeatedly test the system under

study after making limited, controlled changes in it.

There are, of course, circumstances when one cannot isolate the phenomena or when one cannot repeat the measurement over and

over again. In such cases the results may depend in part on the history of a situation. This often occurs in social interactions between

people. For example, when a lawyer makes arguments in front of a jury in court, she or he cannot try other approaches by repeating

the trial over and over again in front of the same jury. In a new trial, the jury composition will be different. Even the same jury

hearing a new set of arguments cannot be expected to forget what they heard before.

VI. Conclusion

The scientific method is intricately associated with science, the process of human inquiry that pervades the modern era on many

levels. While the method appears simple and logical in description, there is perhaps no more complex question than that of knowing

how we come to know things. In this introduction, we have emphasized that the scientific method distinguishes science from other

forms of explanation because of its requirement of systematic experimentation. We have also tried to point out some of the criteria

and practices developed by scientists to reduce the influence of individual or social bias on scientific findings. Further investigations

of the scientific method and other aspects of scientific practice may be found in the references listed below.