Geometrical optics / by Val H. Mackinney and Harry L. Taylor.

  • Mackinney, Val H., 1791-1868.
Date:
1908
Catalogue details

Licence: In copyright

Credit: Geometrical optics / by Val H. Mackinney and Harry L. Taylor. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    €ct3oe L Geometrical and Physical Optics, Chapter I. CURVATURE SYSTEM AND OPTICAL NOTATION. ^J^H]^]N a stone is tlirown into water we notice that concentric circles of i-ipi)les emanate from tlie point of disturbance, and that any straiglit line from that point to any circle measures the distance of the ripple from the point of origin. Without pressing the analogy too closely we may illustrate the progress of light waves from a luminous point hy this illustration, and as light travels in straight lines a rcijj corresponds to any straight line from the centre, so that it becomes a radius for any given ripple or wave, and is thus the putli of <( ware. Tlie curvature method of treating geometrical 0};tics so simplifies the teaching of this branch of the science, that one wonders why so many writers have given it such slight recognition. This method deals with the subject strictly from the physical stand})oint, and in accordance with the general]v accepted wave theory of light. It lends itself to the satisfactory explanation of the phenomena of })hysical optics, and thus in many instances cumbersome mathematical proofs may be replaced by sim])le reasoning—in conjunction with a graphical representation. Furthermore, it offers an especial advantage because it harmonizes with the s})ectacle-lens notation now used by opticians. The introduction of the curvature method into the present volume wall enable the reader to grasp the subject much more readily and to retain the knowledge so gained. It is evident that we need some unit by means of wliicli we can get a dehnite idea of the value of certain measurements, the simplest of which is that of length. We may express this in the standards known as feet, inches, metres, etc., but in addition we must know the point of oi'igin and the direction of measurement. Optical measurements of distance are now universally made according to the metric system, and specified as so nianv metres (m), centimetres (cm), or millimetres (mm).