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)
or, the points at which the conjugate foci Avill be equally distantfrom the lens is when either of them is double the distance of theprincipal focus. If the radiant is at an infinite distance the rays are parallel; inwhich case the corresponding focus will coincide with the principalfocus. 230… … side, as shown; and when the radiant, L, reaches, or coincides with theprincipal focus, the corresponding focus, (the eye) will be at an infinitedistance, as, in this case, the refracted raj^s will be parallel. If the radiant is nearer to the lens than the principal focus, the rayswill diverge, as…
Physics · Astronomy
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