A treatise on astronomy for the use of colleges and schools (1906)
Godfray, Hugh · London, MacMillan · leaf 110
Micrometer. It is well knownthat when a pencil of common light passes through certaincrystalline substances it undergoes a bifurcation, and twopencils are produced. In uniaxal crystals, such as Icelandspar, one of the pencils is refracted as it would be throughordinary transparent substances, and… … CHAP. VI.j DOUBLE IMAGE MICROMETER. 89 pencils do not separate : this is, when incident perpendicularlyon a surface which is itself perpendicular to the axis ofthe crystal. Now, if we take two triangular prisms of Iceland sparABCG and BCDE, which, byjuxtaposition, form a rectangularparallelepiped…
Astronomy
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