. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. SENSE ORGANS. 1Q$ there is a corresponding focal point in the image, and therefore the image will be a perfect facsimile of the object. Observe, then, (i) the image is inverted. All images made by lenses (dioptric images) are inverted. They must be, because the central ray of the pencil from each radiant passes straight through the lens without bend- ing, and therefore these central rays all cross one another. Fig. 73. at a certain point in the lens called the nodal point. Ob- ser
. Outlines of the comparative physiology and morphology of animals. Anatomy, Comparative; Physiology, Comparative. SENSE ORGANS. 1Q$ there is a corresponding focal point in the image, and therefore the image will be a perfect facsimile of the object. Observe, then, (i) the image is inverted. All images made by lenses (dioptric images) are inverted. They must be, because the central ray of the pencil from each radiant passes straight through the lens without bend- ing, and therefore these central rays all cross one another. Fig. 73. at a certain point in the lens called the nodal point. Ob- serve again (2) that in order to have a sharp image the receiving screen must be exactly at the focus of rays; for nearer than this the rays have not yet come together to a focal point; farther than this they have already crossed and spread out again. Observe (3) that the size of the image will be to that of the object in the exact proportion to their relative distances from the nodal point. (4) Again, as the object comes nearer the lens the image will be thrown farther back, while if the object recedes from the lens the image will approach the lens. (5) It is not every lens that will make a perfect image. It must have a proper shape, and, moreover, it is found that a system of several lenses is better than a single lens. Application of these Principles to the Eye.— Now the eye is an instrument consisting of a system of lenses. The eye therefore forms its images of all ob- jects presented to it. In Fig. 74 rays from the two points A and B of an object A B are brought to focus on. 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 LeConte, Joseph, 1823-1901. New York, D. Appleton and Company
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