Revisiting a Celebrated Bakerian Lecture

This paper revisits the optical contributions of Thomas Young to the theory of diffraction and, in particular, some experiments presented in his celebrated “Bakerian Lecture” of 1803. The major input to re-analyze some of Young’s experiments came by a recent paper appeared on an instructional and pedagogical journal. Diffraction experiments of Thomas Young are here revisited with particular reference to the coherence requirements of the white light source to see and measure diffraction fringes by pins, and in general to consider the difficulties in working in a “camera obscura”. If at the beginning of the nineteenth century, the experiments of Optics in a darkroom were considered “simple”, however they needed rooms about 7 meters long, completely darkened out, with a window mostly exposed to south, a darkened window and a small hole practiced on a dark sheet applied to a hole in the window shutter. Often a heliostat should be placed outside and a mirror inside the room to direct the cone of sunlight. Thomas Young worked only with a mirror interior to the darkened room in order to have a cone of light horizontally directed and moving the mirror at each observation. Today, these requirements are not easy to implement. However, only a single measure by Thomas Young will be repeated under his own conditions with a “reduced darkroom” using internally blackened cardboard tubes.