. Laboratory work in bacteriology. Bacteriology. THE MICROSCOPE. 125 The violet component is bent most, and hence, is brought to a focus at a different point from the red ray, which is bent the. least. The result is a fringe of colors. This is designated as chromatic aber- ration. It is necessary, therefore, to correct the chromatic and spherical aberration, in order to obtain the best optical re- sults. The spherical aberra- tion is partially corrected by means of stops or diaphragms, which hold back the peri- pheral rays, and allow only the central ones to pass through, since these give rise
. Laboratory work in bacteriology. Bacteriology. THE MICROSCOPE. 125 The violet component is bent most, and hence, is brought to a focus at a different point from the red ray, which is bent the. least. The result is a fringe of colors. This is designated as chromatic aber- ration. It is necessary, therefore, to correct the chromatic and spherical aberration, in order to obtain the best optical re- sults. The spherical aberra- tion is partially corrected by means of stops or diaphragms, which hold back the peri- pheral rays, and allow only the central ones to pass through, since these give rise to an almost flat image. Such diaphragms are shown in Fig. 17. The use of flint glass still further, serves to correct this error. The chromatic aberration is more diiificult to correct. The first successful attempt at the correction of chro- matic aberration in an objec- tive, was made by an Italian, Marzoli, in 1811. In other words, 200 years elapsed be- tween the discovery of the compound microscope and the correction of the most serious defect in the working of the objective. This early work, however, seems not to have attracted much attention, and Chevalier, of Paris, was given. Fig. 17. Principle of the compound mi» croscope (Carpenter). F—Object in focus, above this an objective with diaphragm; AB—Real image of F, in opening of dia- phragm; above this a compensation ocular vfhich magnifies the real image AB, thus forming the virtual image Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Novy, Frederick George, 1864- . Ann Arbor [Mich. ] G. Wahr
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