Boulanger binoculars

By utilizaing the telescope with prism-inversion, devised in 1851 by Ignazio Porro (1795-1875), A. A. Boulanger succeeded in producing a binocular of an entirely new type in 1859. But he overlooked the possibility of increasing the distance between the objectives; Camille Nachet introduced this improvement in 1875, but his instruments did not meet with much popularity.
Source: 1911 EB, Vol. 3, Page 950

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