The London, Edinburgh and Dublin philosophical magazine and journal of science . eces D lies inside the eyepiece; andthe diagram &c. will need to be modified accordingly. Phil Mag. S. 5. Vol. 42. No. 259. Dec. 1896. 2 N 502 Dr. Gr. J. Stoney on Microscopic Vision. speak of the grasp of a beam, and of the grasp of the designation is justified, since, as we shall presently see,the quantity designated by it, when it is applied to an ob-jective, is the proper measure of its resolving power, i. e. ofthe minuteness of detail which that objective can reach ; andwhen applied to an indiv
The London, Edinburgh and Dublin philosophical magazine and journal of science . eces D lies inside the eyepiece; andthe diagram &c. will need to be modified accordingly. Phil Mag. S. 5. Vol. 42. No. 259. Dec. 1896. 2 N 502 Dr. Gr. J. Stoney on Microscopic Vision. speak of the grasp of a beam, and of the grasp of the designation is justified, since, as we shall presently see,the quantity designated by it, when it is applied to an ob-jective, is the proper measure of its resolving power, i. e. ofthe minuteness of detail which that objective can reach ; andwhen applied to an individual beam or to its axial ray, itindicates the farthest that two rays of that obliquity can goin the representation of detail, in other words their utmostgrasp. When applied to the most inclined beam in anymeridian plane whose axial ray can be caught by the ob-jective, it measures the grasp of the objective, and mayconveniently be represented by G, and it may be symbolizedby g when applied to any less inclined beam. When the beams are in the same meridian but differently. inclined, we may proceed as follows :—Let kg be the front ofthe objective, o the middle of image C, and ob and oh theaxial rays of two beams lying in the same meridian beams, if reversed, will under ordinary circumstances(i. e. if the transversals are not in altogether discordantpositions) produce a ruling* in image C. The spacing of thisruling is given by the formula V = a (sin a + sin a), where a is the spacing of the ruling, V the wave-length inmedium c, and where a and a are counted as positive whenon opposite sides of the vertical. Multiply both sides by n,the index of refraction of medium c. Then n\ = a(n sina-fn sin a), * To prevent misapprehension it may be well to call attention to thecircumstance that this ruling may have a very brief existence—lasting forsomething like one foot of time in cosmic measure, see footnote, p. 425—and may be succeeded on the image-plane by other rulings
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