Elements of natural philosophy (Volume 2-3) (1850)
Bartlett, W. H. C. (William Holms Chambers), 1804-1893 · New York : Barnes · leaf 213
.bor ^ —, or ii f<Fu,f will be positive, and the ver- Beai radiants gency of the deviated Avitliin the ipai focus; ra.Ys W1^ be positive.That is, if the wave pro-ceed from a point infront and situated be- prmcij Fig. 28. … ELEMENTS OF OPTICS. 205 tween the lens and the principal focus, it will, after Give virtual focLdeviation, proceed from some other point in front, and thefocus will be virtual. Fo] 1 1 _ - j? 1 f = 0, or/ = oo Fis. 29.
Mechanics · Acoustics · Optics
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