ion it will be seen that s is either negative or, if positive, it is greater 118 LIGHT. [CH. VI than r, so that in either case is positive and the focal length is positive; for a convex lens either r is negative, or s is less than r, thusthe focal length is negative. 73. Forms of lenses. In fig.… … plane, while (c) is a concave meniscus, the second face isconvex outwards but its radius is greater than that of thefirst face, so that the lens is thinnest at the centre. In allcases the principal focus is virtual and the focal lengthpositive. In fig. 88, are given three sections of convex lenses,…
Heat · Light
Internet Archive · California Digital Library · Public Domain Mark 1.0. Free to use for anything.
