. Laboratory work in bacteriology. Bacteriology. 124 BACTERIOLOGY. image, inverted and reversed, lies inside of tlie principal focus of the eye-piece, and the rays of light leave it as if they came from a real object. If a screen was placed at this point, it would show an image. Since this image lies inside of the principal focus, it becomes magnified by the eye-piece (E), and the virtual image (C D) is produced. It has been, not inaptly, said that " a compound microscope is a simple microscope applied, not to the object, but to its image already magnified by the first ;. Fig. i
. Laboratory work in bacteriology. Bacteriology. 124 BACTERIOLOGY. image, inverted and reversed, lies inside of tlie principal focus of the eye-piece, and the rays of light leave it as if they came from a real object. If a screen was placed at this point, it would show an image. Since this image lies inside of the principal focus, it becomes magnified by the eye-piece (E), and the virtual image (C D) is produced. It has been, not inaptly, said that " a compound microscope is a simple microscope applied, not to the object, but to its image already magnified by the first ;. Fig. i6. Real image (Carpenter). The single lens naturally represent the earliest form of the microscope. The English monk, Roger Bacon, in 1276, appears to have been the first to recognize the peculiar properties of a lens. It was he who applied the new knowl- edge to the construction of spectacles. It was not, how- ever, till the beginning of the 17th century, that the micro- scope was sufficiently perfected to bring about the discov- ery of the existence of microscopic life. The discovery of the compound microscope may be said to have been made by Galileo in 1610, although it is probable that others may have antedated him by a few years. The early compound microscope consisted of a single lens for an objective, and of another single lens for an eye-piece. Such an instru- ment, necessarily gave very imperfect results. The image produced, by a single lens, is not a perfect reproduction of the original object. All the rays of light do not meet in the same plane, and hence, the image has a spherical appearance. This fault of a lens is known as. spherical aberration. Again, the lens, acting as a prism, de- composes some of the rays of light which pass through 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
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