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Throughout the nineteenth century, Fresnel lenses represented one of the most significant innovations in applied optics, with applications ranging from experimental research to maritime navigation. This paper traces the invention, development, and circulation of these devices, beginning with the work of Augustin-Jean Fresnel and focusing in particular on the large lens employed by Macedonio Melloni in his investigations into the thermal effects of moonlight. These experiments contributed to contemporary debates on the nature of radiant heat and on the relationship between luminous and thermal radiation. By examining both laboratory and navigational applications, the paper highlights the multiple trajectories through which Fresnel lenses shaped nineteenth-century scientific and technological uses of light.
This study also examines the diffusion of Fresnel lenses within the lighthouse network of the Kingdom of the Two Sicilies, highlighting the interactions between physical research, technological innovation, and nineteenth-century Bourbon modernization efforts. Drawing on archival sources, surviving scientific instruments, and technical documentation, the study emphasizes the role of Neapolitan scientific culture in the circulation of optical knowledge and technologies within the broader international scientific and technological landscape.