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36809 results in Cambridge Textbooks

Page 1763 of 1841

  • CHAPTER VII - On the three kinds of commonwealth: democracy, aristocracy and monarchy

  • from Government
  • Thomas Hobbes
  • Edited by Richard Tuck, Michael Silverthorne, McGill University, Montréal
  • Book:
    Hobbes: On the Citizen
    Published online:
    11 May 2019
    Print publication:
    20 August 1998, pp 91-101

  • Summary

    1. So far we have been speaking of the commonwealth by design in general. Now we must speak of its kinds. The differences between commonwealths are derived from the difference in the persons to whom sovereign power is committed. Sovereign power is committed either to one man or to one Assembly or council of many men. Again, an Assembly of many men is either an assembly of all the citizens (so that each of them has the right to vote and can participate in debating issues if he so wishes) or of only a part of the citizens. This is the origin of three kinds of commonwealth: The first is where sovereign power lies with an Assembly in which any citizen has the right to vote; it is called democracy. The second is where sovereign power lies with an Assembly in which not all but only a certain part have a vote; it is called aristocracy. The third is where sovereign power lies with one man; it is called monarchy. In the first, the dominant power is called the people (Δῆμος [populus]; in the second, the nobility [optimates]; in the third, the monarch [monarcha].

    2. The ancient writers on Politics have introduced three other kinds of commonwealth in opposition to these: in opposition to Democracy is Anarchy, or confusion; to Aristocracy, Oligarchy, i.e. government by a few; to Monarchy, Tyranny.

  • Preface to the Readers

  • from Philosophical Elements: On the Citizen
  • Thomas Hobbes
  • Edited by Richard Tuck, Michael Silverthorne, McGill University, Montréal
  • Book:
    Hobbes: On the Citizen
    Published online:
    11 May 2019
    Print publication:
    20 August 1998, pp 7-16

  • Summary

    [1] I promise you, Readers, all that is usually thought to encourage attentive Reading: an important and useful Subject, a correct Method in the treatment of it, a good reason and an honest purpose in the writing and good sense in the writer; and in this Preface I offer you a brief view of it all. This book sets out men's duties, first as men, then as citizens and lastly as Christians. These duties constitute the elements of the law of nature and of nations, the origin and force of justice, and the essence of the Christian Religion (so far as the limits of my design allow).

    [2] The wise men of remotest antiquity believed that this kind of teaching (with the exception of anything relating to the Christian Religion) should be given to posterity only in the pretty forms of poetry or in the shadowy outlines of Allegory, as if to prevent what one might call the high and holy mystery of government from being contaminated by the debates of private men. Philosophers meanwhile were active, some in observing the motions and shapes of things to mankind's great benefit, others in contemplating the natures and causes of things, which did man no harm. In the following period Socrates is said to have been the first to fall in love with this civil science; it had not yet been conceived as a whole at the time but was, so to speak, showing a bit of itself through the clouds in the matter of civil government.

  • CHAPTER XII - On the internal causes which tend to dissolve a commonwealth

  • from Government
  • Thomas Hobbes
  • Edited by Richard Tuck, Michael Silverthorne, McGill University, Montréal
  • Book:
    Hobbes: On the Citizen
    Published online:
    11 May 2019
    Print publication:
    20 August 1998, pp 131-141

  • Summary

    1. To this point we have been speaking of the causes of the formation of commonwealths, of the agreements on which they rest, and of the rights of sovereigns over citizens. Now we must speak briefly of the causes of the dissolution of commonwealths, or the causes of sedition. In the motion of natural bodies we have three things to consider: the internal disposition by which bodies are capable of making motion; the external Agent, by which a certain, specific motion is actually produced; and the action itself. So likewise in a commonwealth, there are three things to look at when the citizens are in an uproar: first, the doctrines and passions inimical to peace, by which the minds of individuals are given a certain disposition; second, what sort of men take people who are already disposed to rebellion and violence, and incite, assemble and direct them; and third, the means by which it is done, or faction itself. Of doctrines that dispose men to sedition, the first, without question, is: that knowledge of good and evil is a matter for individuals. We allowed that this was true in the natural state; in fact we proved it (1.9); for in a natural state, individuals live by equal right, and have not submitted by their own agreement to other men's power. But in the civil state it is false.

  • CHAPTER XV - On the kingdom of God by nature

  • from Religion
  • Thomas Hobbes
  • Edited by Richard Tuck, Michael Silverthorne, McGill University, Montréal
  • Book:
    Hobbes: On the Citizen
    Published online:
    11 May 2019
    Print publication:
    20 August 1998, pp 171-186

  • Summary

    1. In the previous pages we have proved from reason and from the testimony of holy scripture that a state of nature, a condition, that is, of absolute liberty like that of men who are neither Sovereigns nor Subjects, is Anarchy and a state of enmity; that the precepts for avoiding such a state are the laws of nature; that a commonwealth cannot exist without sovereign power; and that the holder of sovereign power is owed simple obedience, that is, obedience in all things consistent with God's commands. Only one thing more is needed to complete our knowledge of our civil duty: we must know what the laws or commands of God are. Otherwise we cannot know whether what we are ordered to do by the authority of the civil power is against God's laws or not. And as a result, inevitably, we would either defy God's majesty by obeying the commonwealth too strictly, or slip into confrontation with the commonwealth in our anxiety not to offend God. To avoid both these rocks, we need to know the Divine laws; but as knowledge of a Kingdom's laws depends on a knowledge of the Kingdom, we must speak in what follows of the Kingdom of God.

    2. At Psalm 96.1 the Psalmist says: The Lord Reigns, let the earth rejoice. Again the Psalmist says (Psalm 98.1): the Lord Reigns, though the peoples rage; he sits upon the Cherubim, though the earth be moved.

  • CHAPTER XVIII - On what is necessary for entry into the Kingdom of Heaven

  • from Religion
  • Thomas Hobbes
  • Edited by Richard Tuck, Michael Silverthorne, McGill University, Montréal
  • Book:
    Hobbes: On the Citizen
    Published online:
    11 May 2019
    Print publication:
    20 August 1998, pp 234-247

  • Summary

    1. It has always been an acknowledged truth that all authority in secular matters derives from the authority of the holder of sovereign power, whether that be a man or a group of men. It is clear from what has just been said that in spiritual matters it depends upon the authority of a Church; it will also be clear that every Christian commonwealth is a Church endowed with this kind of authority. From which even the dullest may conclude that in a Christian commonwealth (i.e. in a commonwealth where sovereignty is held by a Christian Prince or Christian group) all power, both secular and spiritual, is united under Christ; and therefore they must be obeyed in all things. On the other hand, because one must obey God rather than man, a difficulty has arisen as to how obedience can be safely offered if an order is given to do something which christ forbids. The reason for the difficulty is that God no longer speaks to us in a living voice through christ and the Prophets, but by the holy scriptures, which are understood differently by different people. Men know very well what kings and the congregated Church command, but they do not know whether what they command is against God's orders or not. Their obedience wavers between the penalties of temporal and spiritual death; they attempt to sail between Scylla and Charybdis; and often fall foul of both.

  • Chapter 1 - Meaning

  • from Part I - Practice
  • Etienne Wenger
  • Book:
    Communities of Practice
    Published online:
    05 July 2013
    Print publication:
    28 July 1998, pp 51-71

  • Summary

    Our attempts to understand human life open a vast space of relevant questions – from the origin of the universe to the workings of the brain, from the details of every thought to the purpose of life. In this vast space of questions, the concept of practice is useful for addressing a specific slice: a focus on the experience of meaningfulness. Practice is, first and foremost, a process by which we can experience the world and our engagement with it as meaningful.

    Of course, in order to engage in practice, we must be alive in a world in which we can act and interact. We must have a body with a brain that is functioning well enough to participate in social communities. We must have ways to communicate with one another. But a focus on practice is not merely a functional perspective on human activities, even activities involving multiple individuals. It does not address simply the mechanics of getting something done, individually or in groups; it is not a mechanical perspective. It includes not just bodies (or even coordinated bodies) and not just brains (even coordinated ones), but moreover that which gives meaning to the motions of bodies and the workings of brains.

    Let me illustrate this point by analogy to a work of art. There are all sorts of mechanics involved in producing a painting: a canvas, brushes, color pigments, and sophisticated techniques. The image itself is but a thin veneer. Yet in the end, for the painter and for the viewer, it is the painting as an experience of meaning that counts. Similarly, in the pursuit of our enterprises, we engage in all sorts of activities with complex bodies that are the result of millenia of evolution. Still, in the end, it is the meanings we produce that matter.

  • 2 - FM receivers

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 49-108

  • Summary

    Superheterodyning revisited

    Just as the superheterodyne receiver dominates AM receiver design, so it dominates FM receiver design and has done so since its infancy. It is interesting to note that Major Edwin Armstrong, who invented the superheterodyne principle, also invented FM. This invention arose from his investigation of the causes and elimination of noise in AM receivers.

    Because the frequency spectrum of FM is so much wider than that for AM, the FM band is placed much higher in the frequency spectrum. Broadcast FM stations are assigned frequency slots 0.2 MHz wide - 20 times that for commercial AM. These stations have carrier frequencies between 87.9 and 107.9 MHz. Thus both the AM and FM broadcast bands will accommodate about 100 discrete channels. The IF frequency used for broadcast FM receivers is 10.7 MHz.

    As was the case for AM, it will be instructive to look at the spectral energy diagram for sinusoidal modulation (Fig. 2.1). As was also the case for AM, the mixing process results in two complete FM signals. The difference frequencies are clustered about 10.7 MHz and pass on into the IF amplifier.

    Exercise 2.1 Assuming the station tuned to has a carrier at 99.3 MHz, find the frequency about which the sum frequencies are clustered.

    As might be expected, the sum frequencies are eliminated by the tuned amplifier. All of the original FM information is thus in the IF signal.

    The limiting principle

    Because all of the information in an FM signal is encoded as frequency variation, it is a foregone conclusion that any variation of amplitude represents noise. This source of noise can be virtually eliminated by passing the FM signal through a limiter prior to detection. A simple and effective limiter consists of an amplifier stage driven to saturation on one polarity of signal swing and cutoff on the other polarity. There will be, of course, a finite slope to the rise and fall of the squaredoff output, but the greater the overdrive the FM signal presents to the limiter, the more nearly square will be its output. Limiters are also cascaded to give more perfect (or harder) limiting.

    The FM detector principle

    FM detectors are usually called discriminators or demodulators. Unlike AM, where the form of the detector is almost universal, there is a wide variety of workable FM detectors.

  • 1 - AM receivers

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 1-48

  • Summary

    The crystal set

    From both the conceptual and historical points of view, our study of AM receivers must start with the “crystal set.” This is the simplest AM receiver, consisting of only three essentials: a tuned circuit, a detector, and a transducer (usually headphones or an earphone) to provide sound output. A simple crystal set schematic is shown in Fig. 1.1. To get usable volume, it is generally necessary to use a long (50 or more) antenna and an earth ground. The capacitor is variable so that the parallel resonant tuned circuit composed of it and the inductance L can tune over the AM broadcast band (535-1,705 kHz). Two types of variable capacitors used for tuning are shown in Fig. 1.2.

    Exercise 1.1 A once-common variable capacitor has a maximum capacitance of 365 pF.

    (a) What must the inductance be if the receiver is to tune the entire AM band?

    (b) What must the minimum value of the variable capacitance be to tune the entire AM band?

    The sound section of any consumer electronic equipment is referred to as audio, and the amplifier that amplifies electrical signals in the range of human hearing is called an audio amplifier.

    The diode in Fig. 1.1 demodulates the audio signal from the AM carrier and feeds it into the headphones.

    The crystal set has two serious shortcomings: poor selectivity and poor sensitivity. Selectivity is the ability to separate two stations whose carrier frequencies are close together - especially if one of them delivers significantly more signal to your antenna than the other. If you thought upon reading this definition that selectivity must depend on the Q of the tuned circuit, you are absolutely correct.

    Sensitivity is a measure of how strong a signal must be delivered to the antenna for a radio to receive it properly. It is usually expressed in /∧volts/meter needed to drive the radio receiver to full output for AM. For FM, it is usually given as /xvolts needed for full quieting. Note that for AM the units of sensitivity are those of electric field. In other words, the sensitivity specification is a measure of the E field strength of the station's transmitted electromagnetic wave needed by the receiver's antenna.

  • Coda II: Learning communities

  • from Part II - Identity
  • Etienne Wenger
  • Book:
    Communities of Practice
    Published online:
    05 July 2013
    Print publication:
    28 July 1998, pp 214-222

  • Summary

    I have argued in Coda I that learning involves an interaction between experience and competence. In communities of practice, the definition of competence and the production of experience are in very close interaction. Mutual engagement in a shared practice can thus be an intricate process of constant fine tuning between experience and competence. Because this process goes both ways, communities of practice are not only a context for the learning of newcomers but also, and for the same reasons, a context for new insights to be transformed into knowledge.

    1. • On the one hand, a community of practice is a living context that can give newcomers access to competence and also invite a personal experience of engagement by which to incorporate that competence into an identity of participation. When these conditions are in place, communities of practice are a privileged locus for the acquisition of knowledge.

    2. • On the other hand, a well-functioning community of practice is a good context to explore radically new insights without becoming fools or stuck in some dead end. A history of mutual engagement around a joint enterprise is an ideal context for this kind of leading-edge learning, which requires a strong bond of communal competence along with a deep respect for the particularity of experience. When these conditions are in place, communities of practice are a privileged locus for the creation of knowledge.

  • 10 - Telephones

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 509-542

  • Summary

    Until the FCC removed the ban on connecting non-AT&T equipment to the phone lines, few people would have thought of the telephone as a consumer electronic item. Now, however, there can be little doubt that it is one. Not only did this decision unchain the creative genius of free enterprise, but it coincided in time with the emerging availability of inexpensive MSI and LSI chips. The result has been a proliferation of phones and features undreamed of just twenty years ago. The Bell System's development of Touch-Tone® dialing led to the development of the DTMF (dual-tone, multi-frequency) encoder and, later, decoder chips. Sharply declining prices on digital memory chips led to their incorporation in many phones for phone number storage and rapid dialing. Phones with memory may be broken down into three groups:

  • (1) Those that can store just a single number - the last one dialed. If that number is busy, it can be redialed with a single button.

  • (2) Those that store two to ten numbers. These numbers can be dialed by pushing just one of the digit buttons.

  • (3) Those that can store more than ten numbers. These numbers can be dialed only by pressing two buttons in sequence to form a two-decimaldigit code.

    • Anyone who has ever listened to a phone conversation where the speaker tried to make a comment while covering the receiver with his hand knows that this does a very poor job of masking the sound. It is therefore surprising that a concept as simple as the privacy or mute switch did not come into wide use until the lines were made available to all equipment that met phone company specifications.

    Speakerphones have existed for some time, but they tended to be prone to acoustic feedback. Current versions, however, electronically sense where the input is coming from and open the channel only in the direction it needs to go. When the speaker changes, signal flow in the opposite direction is enabled.

    Cordless phones have benefited from inexpensive transmitter and receiver ICs and have declined in price to where they are now a popular option. They are almost too popular, in fact. In some wealthy neighborhoods, there have been so many cordless phones that two related problems have become evident. The first is interference between phones, and the second is eavesdropping.

  • Series forward

  • Etienne Wenger
  • Book:
    Communities of Practice
    Published online:
    05 July 2013
    Print publication:
    28 July 1998, pp xi-xii

  • Summary

    This series for Cambridge University Press is becoming widely known as an international forum for studies of situated learning and cognition.

    Innovative contributions are being made by anthropology, by cognitive, developmental, and cultural psychology, by computer science, by education, and by social theory. These contributions are providing the basis for new ways of understanding the social, historical, and contextual nature of the learning, thinking, and practice that emerges from human activity. The empirical settings of these research inquiries range from the classroom to the workplace, to the high technology office, and to learning in the streets and in other communities of practice.

    The situated nature of learning and remembering through activity is a central fact. It may appear obvious that human minds develop in social situations and extend their sphere of activity and communicative competencies. But cognitive theories of knowledge representation and learning alone have not provided sufficient insight into these relationships.

    This series was born of the conviction that new and exciting interdisciplinary syntheses are underway as scholars and practitioners from diverse fields seek to develop theory and empirical investigations adequate for characterizing the complex relations of social and mental life, and for understanding successful learning wherever it occurs. The series invites contributions that advance our understanding of these seminal issues.

  • Chapter 4 - Boundary

  • from Part I - Practice
  • Etienne Wenger
  • Book:
    Communities of Practice
    Published online:
    05 July 2013
    Print publication:
    28 July 1998, pp 103-121

  • Summary

    In the previous chapter, I characterized communities of practice as shared histories of learning. Over time, such histories create discontinuities between those who have been participating and those who have not. These discontinuities are revealed by the learning involved in crossing them: moving from one community of practice to another can demand quite a transformation. But practice does not create only boundaries. At the same time as boundaries form, communities of practice develop ways of maintaining connections with the rest of the world.

    So far, I have focused almost exclusively on communities of practice as if they were isolated. But that focus was artificial. Communities of practice cannot be considered in isolation from the rest of the world, or understood independently of other practices. Their various enterprises are closely interconnected. Their members and their artifacts are not theirs alone. Their histories are not just internal; they are histories of articulation with the rest of the world.

    As a result, engagement in practice entails engagement in these external relations. For a job like claims processing, which is considered by many to be relatively narrow, the range of related communities of practice as well as constituencies without a shared practice is actually rather complex. It involves, among others, claims technicians, underwriters, system designers, and various levels of management at Alinsu; beyond the company, there are other claims processors, patients, benefit representatives, accounting clerks, and a variety of medical and legal professionals.

  • 8 - Video cassette recorders

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 345-458

  • Summary

    Although recorders capable of recording a TV signal on magnetic tape have been available since the early 1950s and vidéocassette recorders have been since the early 1970s, they never became a consumer item until 1975, when Sony introduced the Betamax VCR. Earlier units were generally too complex, too expensive, and too voracious in their appetite for tape. The first Betamax units could record for one hour on a cassette, making them almost as easy to use as an audio tape recorder. Two years later, Matsushita introduced the VHS (Video Home System) VCR, which boasted recording times of two or four hours on a somewhat larger cassette. The Betamax system was then modified to allow two hours of recording. Subsequently VHS achieved a six-hour record time and Beta got up to three hours. For both machines, the longer record time yielded slightly inferior picture quality relative to the shorter record times. Although both systems used the same general principles in their electronics, they were not compatible either mechanically or electrically. If both systems were played at their fastest speed (one-hour play time for Beta; two hours for VHS), the Beta probably produced a slightly better picture quality, but if both were operated in the two-hour mode, the VHS picture was generally better. The fundamental reason for this is that the Beta cassette is smaller and simply cannot hold as much tape as the VHS cassette does. Thus the Beta achieved the two- and threehour modes by slowing down the tape speed. This hurt high-frequency response and so picture details were lost.

    Although there were a number of more esoteric differences between the Beta and VHS systems such as tape tension (Beta lower in record and playback; VHS lower in fast forward and reverse), it can hardly be maintained that the chief issue in the minds of most consumers was anything but the longer record time of the VHS. This led to the situation in 1985 that all manufacturers of the Beta system except Sony had either switched to the VHS system or were “hedging their bets” by manufacturing both VHS and Beta systems. The dominance of VHS over Beta is now total. Virtually no tapes are produced in Beta format any longer. For these reasons, we will direct our attention exclusively to the VHS system.

Page 1763 of 1841