Esta introdução descreve os mais importantes dados biográficos da vida e da obra do físico teórico austríaco Ludwig Boltzmann (1844-1906). As principais contribuições científicas de Boltzmann situam-se nos domínios da teoria cinética dos gases e mecânica estatística, da qual ele foi um dos fundadores. A tese de que as teorias científicas são representações dos fenômenos naturais é encontrada em todos os artigos de Boltzmann. No verbete "modelo", ela é apresentada de modo mais organizado, o que o torna uma peça fundamental (...) para a compreensão do pensamento filosófico do físico austríaco. O verbete, publicado na famosa enciclopédia Britannica, foi escrito para o público em geral. Ainda assim, Boltzmann não se eximiu de tomar partido em favor do uso de modelos. Estes últimos não apenas seriam inevitáveis, mas necessários, uma vez que tornavam possível o aperfeiçoamento contínuo da ciência. This introduction describes the most important biographical details of the life and work of the Austrian theoretical physicist Ludwig Boltzmann (1844-1906). The main scientific contributions of Boltzmann can be found in areas such as the kinetic theory of gases and statistical mechanics, of which he was one of the co-founders. The thesis that scientific theories are representations of natural phenomena is found in all philosophical articles by Boltzmann. In the entry "model", published in the celebrated Encyclopedia Britannica, the thesis is presented in a more organized way, making it the keystone to understand the philosophical thought of the Austrian physicist. Although the entry was written for the general public, in it Boltzmann did not refrain from taking sides as far as the use of models is concerned. According to him, the latter would not only be inevitable, but in fact necessary, since they would made possible the continuous improvement of science. (shrink)

The article investigates the different conceptions of stability found in qualitative studies on the solutions of differential equations. We start from the definitions proposed by Poincaré and criticized by Birkhoff for not being fully qualitative, and show that the clarification of the criterion for stating that a property is qualitative comes precisely with Birkhoff. In addition, we note that the stability conceptions of Lyapunov and Levi-Civita are also important in this transition from the appearance of the first qualitative tools in (...) the study of differential equations to the definition of stability in use in dynamical systems theory. The history of stability can help to explain the meaning of the word “qualitative” in this context. (shrink)

Este artigo descreve o modo pelo qual a noção de modelo começou a ingressar na ciência, em particular na física, no final do século XIX. Este é talvez o primeiro domínio científico a fazer uso explícito e consciente dessa noção, para o qual o uso de modelos significou o abandono de toda e qualquer tentativa de representar fielmente os fenômenos naturais. Em questão, estava a representação dos fenômenos elétricos e magnéticos por meio de analogias. This article describes the way in (...) which the idea of model began to be discussed in science, in particular in physics, towards the end of the 19th century. Physics is perhaps the first scientific domain that explicitly and consciously made use of models in a way that was understood to involve abandoning any attempt faithfully to represent natural phenomena. The representation of electromagnetic phenomena by means of analogies was in question. (shrink)