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From an acoustical point of view, bone is a complex medium as it is heterogeneous, anisotropic and viscoelastic. This chapter reviews the basic notions of physical acoustics which are necessary to tackle the problem of the ultrasonic propagation in bone, in the perspective of the application of quantitative ultrasound (QUS) techniques to bone characterization. The first section introduces the basic phenomena related to the field of medical ultrasound. Basic description of wave propagation is introduced. Mechanical bases are necessary to understand the elastodynamic nature of the interaction between bone and ultrasound. The physical determinants of the speed of sound of the different types of waves corresponding to the propagation in a liquid and in a solid are considered. The effects of boundary conditions (guided waves) are also detailed. The second section describes the physical interaction between an ultrasonic wave and bone tissue, by introducing reflection/refraction, attenuation and scattering phenomena. [ABSTRACT FROM AUTHOR]

It is commonly believed that the longitudinal axes of churches extend exactly in an east-west direction. However, thorough investigations have shown that this is not always correct; rather, both southern and northern deviations of up to about 25° can occur. The angular deviation between the church axis and true east is called the Holy Alignment. This present study presents the possibility that the nave is oriented towards the direction of the sun-rising point on the name day of the patron saint of the church. If several saints share the patronage, the Holy Alignment equals the algebraic sum of the angular distances for each saint. The orientation of a nave can be analyzed by means of common mathematical relations used in geodesy, astronomy and gnomonics. In order to perform such an anlysis, it is necessary to know the history of the patronage of the church; the Gauss-Krüger coordinates of the ground plan; and characteristic astronomical quantities at the time the church was built. A calculated example with the saints Andrew, James and Philip for the year 980 illustrates the analysis. An appendix deals with the influence of atmospheric refraction on the apparent altitude of the sun near the horizon. [ABSTRACT FROM AUTHOR]

Like harmony in music; there is a dark inscrutable workmanship that reconciles discordant elements, makes them cling together in one society. The products of the glass maker are often aesthetically pleasing, but it would be unfair to claim that glass is intrinsically more attractive than any other type of material. Rather, by its presence in the family of materials, glass extends the range of useful properties and artistic qualities. As has transpired only recently, glass also extends the range of atomic structures in condensed matter, through its unique lack of order. Indeed, it is this atomic-level attribute, rather than the traditional ones of transparency and brittleness, which is now acknowledged as the defining characteristic of this type of material. Oxide glasses such as the common silicate varieties have been in use for at least 4000 years. Glass beads, dating from about 2500 BC, have been found in Egypt and other parts of the Near East, although exploitation of the plasticity of hot glass is more recent. These oxide materials so dominated the scene that the existence of the glassy state was believed to be intimately connected with the presence of covalent bonds. Glass has long been known to be a supercooled liquid, and covalent bonding was regarded as a prerequisite if crystallization was to be avoided. These attitudes underwent radical revision in the 1960s. With the production of metallic examples, it was suddenly realized that a glass need not be transparent, brittle, or insulating. [ABSTRACT FROM AUTHOR]

Newton's theological manuscripts are concerned principally with two subjects: the interpretation of the prophecies of the Apocalypse and Daniel, and the history of the early Church. These two subjects are linked, but it was as a consequence of his interpretation of the Apocalypse that Newton undertook his study of the history of the Church. The study of prophetic literature was firmly rooted in Cambridge, where this subject was taught by Joseph Mede, author of a Clavis Apocalyptica (or Key to the Apocalypse), a work much used by Newton. [ABSTRACT FROM AUTHOR]

Isaac Newton deserves to be included in a series of companions to major philosophers even though he was not a philosopher in the sense in which Descartes, Locke, and Kant were philosophers. That is, Newton made no direct contributions to epistemology or metaphysics that would warrant his inclusion in the standard list of major philosophers of the seventeenth and eighteenth centuries - Descartes, Spinoza, Locke, Leibniz, Berkeley, Hume, and Kant - or even in a list of other significant philosophers of the era - Bacon, Hobbes, Arnauld, Malebranche, Wolff, and Reid. The contributions to knowledge that made Newton a dominant figure of the last millennium were to science, not to philosophy. By contrast, Galileo, the other legendary scientific figure of the era, not only published the most compelling critique of Aristotelian scholasticism in his Dialogues on the Two Chief World Systems, but in the process turned the issue of the epistemic authority of theology versus the epistemic authority of empirical science into a hallmark of modern times. Although Newton clearly sympathized with Galileo, he wrote virtually nothing critical of the Aristotelian tradition in philosophy, and the immense effort he devoted to theology was aimed not at challenging its epistemic authority, but largely at putting it on a firmer footing. Newton made no direct contributions to philosophy of a similar magnitude. Indeed, from his extant writings alone Newton has more claim to being a major theologian than a major philosopher. [ABSTRACT FROM AUTHOR]

Introduction The eclipse observations made by medieval Arab astronomers are among the most accurate and reliable data from the whole of the pre-telescopic period. Careful records of both solar and lunar eclipses are contained in a number of compendia – some known as zijes (astronomical handbooks containing various tables along with explanatory text). These include measurements of the times of occurrence and other details such as magnitude estimates. Although the main emphasis in this chapter will be on timed data, solar magnitude estimates and horizon observations of eclipses will also be considered. Many of the observations discussed below were investigated by Newcomb (1878) and Newton (1970). However, these authors relied on published translations which sometimes contained significant errors, while their own interpretations are occasionally suspect. Furthermore, in neither case was a direct solution made for ΔT. Sources of data Most of the accessible eclipse observations by medieval Arab astronomers are contained in a single treatise – the zij compiled by the great Cairo astronomer Ibn Yunus, who died in AD 1009 (his date of birth is unknown). A few eclipses are also recorded in works by al-Battani (who lived between AD 850 and 929) and al-Biruni (AD 973–1048). Ibn Yunus cites reports of some thirty solar and lunar eclipses from between AD 829 and 1004. His treatise, dedicated to Caliph al-Hakim, is entitled al-Zij al-Kabir al-Hakimi. [ABSTRACT FROM AUTHOR]

Introduction Despite their relatively low precision, pre-telescopic observations cover a sufficient time-span for long-term trends in the length of day (LOD) to become apparent. These trends cannot be discerned from modern measurements. Here we have the main reason why archaic observations are so important in the study of the Earth's past rotation. The analysis of ancient and medieval eclipse records is just one of several techniques which have been utilised in recent years to investigate variations in the LOD over the historical past. Before discussing in detail the application of eclipse observations to this problem, it is necessary to briefly consider other available methods and to explain why eclipses are to be preferred to other types of data. Observational requirements for determining Δ T in the pre-telescopic period Any early astronomical observation which is of value in studying changes in the LOD in the past must satisfy a wide variety of criteria. These may be listed as follows: (i) The observation must involve at least one of the brighter and more rapidly moving objects in the solar system (i.e. the Moon, Sun or one of the inner planets Mercury, Venus and Mars). (ii) The exact Julian or Gregorian date of the observation must either be specified directly or be able to be determined unambiguously. […] [ABSTRACT FROM AUTHOR]

When Leonhard Euler published his treatise ‘Nova theoria lucis et colorum’ (A new theory of light and colours) in 1746, he made a contribution to the medium tradition in physical optics that was without parallel in the eighteenth century. The ‘Nova theoria’ constitutes the most lucid, comprehensive, and systematic medium theory of that century. The significance of Euler's theory can be gauged partly from the fact that it was so widely discussed. No earlier attempts to provide an alternative to the theories developing within the emission tradition had stimulated pens to the same extent as Euler's ‘Nova theoria’. It is remarkable that a relatively short treatise published as part of a collection of articles on a range of subjects created such resonances, and all the more so when we compare this reaction with the limited response to Huygens' Traite - a complete book - and with the way in which Johann II Bernoulli's prize essay was virtually ignored. A partial explanation no doubt lies in the quality of Euler's work, while his authority also made it difficult to ignore his ‘new theory’. Euler was probably the most important, or at any rate the most fecund, exponent of mathematics and natural philosophy in the Enlightenment. Although his accomplishments in mathematics and mechanics are generally known and acknowledged, Euler's contributions to optics have attracted little scholarly attention up to the present. However, his role in the discovery of achromatic lenses has been the subject of historical study. [ABSTRACT FROM AUTHOR]

Introduction In the standard historiography of science the eighteenth century is the period in which the emission conception of light was quite generally accepted, certainly after 1740. Euler is usually mentioned as the exception to this rule. Surveys that are more oriented towards Germany add one or another dissident to the list but leave the image unaltered on the whole: The emission tradition ruled the physical optics roost in the eighteenth century. Apparently the picture of the situation in different countries is to a great extent determined by simply declaring the general picture to be valid for every country, without any thorough investigation of the matter. Britain and Ireland are the only countries on which detailed and systematic research has been carried out. G. N. Cantor has provided an exhaustive survey of optical viewpoints in this region. His results do, it is true, lend nuances to the established image, but they introduce no radical change. In Cantor's book only 9 per cent out of a total of sixty-nine optical theorists from the eighteenth century support a medium theory, while the remaining 91 per cent can be located within the emission tradition. In other words, the historical evidence thus far available confirms the strongly dominant position of the emission tradition in the eighteenth century. Nevertheless, it will be argued in this section that a substantially different view of the matter ought to be given for Germany. [ABSTRACT FROM AUTHOR]