Abstract
LONDON. Optical Society, June 14.—T. Y. Baker: The errors of a reflecting prism. A prism with two reflecting faces designed to fulfil a particular purpose in an optical instrument gives rise to errors due to (a) inaccuracy of manufacture, and (b) inaccuracy in mounting the prism in the instrument. The effects of these errors are investigated.—W. D. Wright: A trichromatic colorimeter with spectral primaries. A spectrometer system is used in which two spectra are formed from the same source. From one, three portions to act as primaries are reflected back through part of the dispersing system, so that the mixing of the three radiations is effected by neutralising the prismatic dispersion by which the colours were first separated. From the other, the test colour and a desaturating colour are selected and mixed in a similar manner, and the composite beams are then brought into a simple bipartite field. The Max-wellian method of observing the field of view lias been adopted without the introduction of rotating parts into the system, and special precautions have been taken to remove stray light.—T. Smith: (1) The theory of aplanatic surfaces. The necessary and sufficient condition that an optical system should have a pair of aplanatic surfaces is that the cikonal of the system can be expressed as a homogeneous function of the first order in three variables. Methods are given for finding the equations of these surfaces when the eikonal is given and for finding the eikonal when the surfaces are given. In general, only one pair of aplanatic surfaces is possible, but in spherically symmetrical systems two pairs are found. (2) The primordial coefficients of asymmetrical lenses. An easily calculable system of sixteen magnitudes is constructed for the representation of the properties of asymmetrical lenses. All equations are expressed in matrix form and an account of the elementary properties of matrices is included. (3) Note on the use of lenses in scries for sight-testing. The series arrangement enables a small number of lenses to be combined to give the correction for any regular defect of form. In general, effective powers are not simply additive, but under certain conditions the error made in regarding them as additive becomes small. With incorrect arrangements serious errors may be made.
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Societies and Academies. Nature 122, 116–119 (1928). https://doi.org/10.1038/122116a0
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DOI: https://doi.org/10.1038/122116a0