According to the art critic Philippe Burty, Meryon used a camera lucida in the production of this print. This optical instrument was invented in 1807 to facilitate the accurate sketching of objects. It consists of a four-sided prism mounted on a small stand above a sheet of paper. By placing the eye close to the upper edge of the prism so that half of the pupil of the eye is over the prism, the artist is able to see a reflected image of the object that appears to be lying on the paper. Meryon used thecamera lucida to trace the image of his subject onto paper, but then altered several details to make the scene fit his personal vision.