The lens presented here belongs to the class of echelon lenses designed by Buffon (1707,1788) and carried out first by Fresnel (1788,1827). It was built by Henry Lepaute in Paris around 1840 to order of Macedonio Melloni (1798,1854). Melloni went to Paris in order to purchase instruments for the newborn Osservatorio Vesuviano ("Vesuvius Observatory") of which in 1839 he had been appointed Director. The lens was used by Melloni for measurements of the radiant heat of the moon. Also, he used echelon lenses for the illumination of the harbour of Naples. The optical system has a 120 cm diameter and is formed by a plano-convex lens of 28 cm diameter surrounded by 9 concentric refracting rings. The focal lenght is about 80 cm. The lens is hinged by its horizontal axis on a strong semicircular rod which in turn is hinged, by its vertical axis, on a short stem held by four sturdy legs. The optical system can therefore rotate around both axes. The rotation angles may be read on two circular scales. Some refracting rings are unfortunately chipped but on the whole the lens is in good repair. Overall height 180 cm, with the lens in vertical position. Signed: "Henry Lapaute, rue S. Honore 247, ˆ Paris".
back to Optics