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Fossil Bones. 287 of effect. The chemical substance upon which the light acts, according to M. DaguerrCs method, is laid upon sheets of copper, which~ for the draw, ing exhibited on Saturday, were about nine or ten inches by six or seven inches. The expense of such plates M. Daguerre esttmate~ at about $ ft. 50e. each, but he expects that considerable reductions may be ultimately made in their cost, and that the improvement of his method will render it applicable to other substances notdoi:10.1016/s0016-0032(39)91608-x fatcat:img2n2z4gvdxzanpn777uc2f4e