In 1783 John Michell published a note entitled ‘On the Means of Discovering the Distance, Magnitude etc. of the Fixed Stars, in Consequence of the Diminution of the Velocity of their Light’, but it was Christian Doppler who in 1842 for the first time formulated the principle : If a source of sound or light is in motion relative to an observer, or an observer in motion relative to a source, the period of the waves received by the observer will (...) be different from the period of the waves emitted by the source. The acoustical Doppler principle was verified in 1845 by Buys-Ballot's experiments and by Ernst Mach ). H. Fizeau proposed to verify the optical Doppler principle by measuring the shift of lines in the spectra of stars . This was carried out by William Huggins , and H. C. Vogel and led to exact results in 1892. The Doppler effect with canal rays was shown by Johannes Stark in 1905. (shrink)

This article describes the phenomenon of knowledge building in online environments. Knowledge building is a process within a community, which leads to the development of knowledge. In order to analyze this process, we will look into the ways in which individuals interact with the collective as a whole. For this purpose, the psychic and social systems, which are involved here are regarded as meaning-based systems in the sense of Luhmann’s systems theory—open to the environment, but operatively closed. The respective modes (...) of operation of psychic and social systems will be examined, and “structural coupling” between these systems described. Another characteristic of knowledge-building communities is self-organization, which is described here in the sense of autopoiesis. A pivotal task, which knowledge-building communities have to tackle, is to handle complexity and reach common understanding. These aspects will also be described using conceptualizations of Luhmann’s systems theory, illustrated by many examples. (shrink)

The work of the Bohemian chemist Franz Wald seems to be unknown in the history of science. In this paper some of Wald's these concerning the foundation of chemical theory are discussed in connexion with reflexions given in unpublished letters, which Wald wrote to Ernst Mach during the years 1896–1907.