disclose only the configuration in plan and relief not the internal structure.
A comparison of the white blood corpuscles in Figs. a, e or h, Plate III, with the same corpuscles in Fig. c on the same Plate, will bring this point out clearly.
7. Advantages and disadvantages of the different types of pictures from the point of view of their greater or less liability to be vitiated by fallacy.
Reference may be made here to two of the more important fallacies which come into consideration.
A. Misprision of Focus. We may denote by the term misprision of focus the error we fall into when, misled by the sharpness of the image obtained, we erroneously assume that we are focussed upon the object, and that the image which is under consideration furnishes a correct representation of the disposition of the radiant points in the object. This fallacy is incident in particular in the microscopic outline picture, which is, as we shall see, a picture produced by reflection and refraction.
We lapse into the fallacy of misprision of focus.
(1) When we refer to one and the same optical plane elements which are in reality disposed upon different optical planes.
(2) When we mistake for the system of radiant points which is positioned in the object itself—we may speak of this as the fundamental picture—a system of radiant points—we may speak of this as the phantom or derivative picture—formed closer to the eye by the intersection of the rays proceeding from the radiant points aforementioned.
(3) When, by reason of a defect of accommodation, or in the case where a microscope is employed by reason of its being focussed on a plane lying on the further side from the object, a geometrical pattern is represented upon the retina by a pattern of diffusion discs which reproduces the original pattern somewhat as a negative does a positive.
The first variety of the fallacy of misprision of focus finds illustration—
(a) In the fact that two systems of lines disposed in reality upon separate horizontal planes may, in the case where they cross each other at right angles, be interpreted by the eye as constituting a system of squares ; and
(b) In the fact that oxalate of lime crystals present, as seen under a low magnifying power, the envelope-shaped appearance
