Johnson's natural philosophy and key to philosophical charts : illustrated with 500 cuts; being reduced photographic copies of all the diagrams contained in the author's philosophical series of indestructible school charts ; for the use of schools and families (1878)
quidistantbetween the mirror and the centreof the sphere, of which the mirrorforms a part. In the diagram, T represents thecentre and F the principal focus.The central line passing throughthe centre and focus is the axis.The dotted lines from the centreto the mirror are perpendicular tothe mirror.… … Converging rays and virtual focus (Fig. 18).—If the radiantpoint passes from the principal focus, F, toward the mirror, as to f,the reflected rays, N and II, will diverge, as though emanating from apoint behind the mirror called the virtual focus; and convergingrays, as II and N, falling upon the…
Physics · Astronomy
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