[21] “Journal of the Royal Microscopical Society, 1880,” p. 1050.
[22] Apo-chromatic, from the Greek, signifying freedom from colour.
[23] Prof. Abbe “On Stephenson’s System of Homogeneous Immersion for Microscope Objectives,” “Journal of the Royal Microscopical Society,” II. (1879), p. 256, and on “The Essence of Homogeneous Immersion,” Ibid., I. (1881), p. 131.
[24] Reichert, in his catalogue, does not clearly indicate what the initial powers of his eye-pieces are.
[25] Messrs. Ross have two series of eye-pieces, both Huyghenian. One series is for use with the English 10-inch tube-body, and is distinguished by Roman letters, and the other by numerals, and made as is usual on the Continent, and for use with the shorter tube-body 6½-inch. The initial powers given in the table are for the 10-inch tube, and for the shorter must be read as follows:—
| 1 | 2 | 3 | 4 | } | with 6½-inch tube. |
| 4 | 6 | 8 | 12 | } |
[26] This centring-glass consists of a tubular cap with a minute aperture, containing two plano-convex lenses, so adjusted that the image of the aperture in the object-glass and the images of the aperture of the lenses and the diaphragms contained in the tube which holds the illuminating combination, may be all in focus at the same time, so that by the same adjustment they may be brought sufficiently near to recognise their centricity.
[27] Summary of the value of parabolic illumination and immersion illuminators, by the late Mr. J. Mayall, will be found on p. 27, “Journal of the Royal Microscopical Society” (1879).
[28] Messrs. Baker and Swift have constructed lamps with removal and fixed achromatic bull’s-eye lenses in gymbal, and changeable tinted glass screens. Either of these will add to the usefulness of the lamp in bacteriological research work. Baker’s is constructed on the Herschel doublet formula, and should therefore be free from aberration. It is mounted on a heavy brass tripod foot, has vertical and horizontal movements by rack and pinion, brass reservoir, with screw opening for filling, metal chimney to take 3 × 1½-inch glass slip, removable frame for carrying tinted glass screens, &c.
[29] “Journal of the Royal Microscopical Society,” p. 365, 1896.