Universal exhibitions held during the second half of the nineteenth century represented one of the most characteristic events of Western society, of its achievements and of its conquests. Science and technology obviously played a significant role in these exhibitions. Science was often represented by instruments and didactic displays. However, if scientific instruments and apparatus could still arouse a certain interest on the part of the fair-going public between the 1850s and the early 1870s, during the last decades of the century exhibition visitors frequently expected to be amused rather than educated. Therefore, science often became the pretext for realizing large-scale, spectacular attractions, reaching their most theatrical manifestation in the Palais de l’Optique erected on the occasion of the 1900 Parisian Exposition universelle. Nevertheless, the role of exhibitions in popularising and diffusing science was far from being anecdotic only. These events constituted ideal arenas for organising important scientific congresses, and also stimulated the foundation of some of the most significant museums of science and technology.