he same point but thatthey intersect the line APQ in a series of points; there isstrictly speaking no geometrical image of the point P. Ifhowever we confine ourselves to a small pencil of rays fallingalmost normally on the surface in the neighbourhood of thepoint A, the foot of the normal from P,… … B 76 LIGHT. [CH. IV we have always RQ=p.RP, PR being any incident ray;now Q is the position of Q when R is very close to A, andthen RP is very nearly equal to A P and RQ to A Q so that wehave approximately AQ = \iAP. Thus a small pencil of raysfrom P, the axis of which is incident normally at A,…
Heat · Light
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