Abstract
IT is well known in optics that, if µr is the refractive index of the rth medium of a co-axial system, hr is the height of the image of a given object from the axis in the same medium, and αr is the angle a selected ray makes with the axis at the image plane, then is invariant (Smith–Lagrange invariant). The choice of sin αr or tan αr varies with different authors. The relation holds in all systems where sin α and tan α are indistinguishable.
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ROGERS, G. An Extended Smith–Lagrange Invariant. Nature 172, 118 (1953). https://doi.org/10.1038/172118a0
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DOI: https://doi.org/10.1038/172118a0
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