Page:Principles of Microscope.djvu/27

Rh image by antipoints which are larger than those which correspond to the full aperture of the objective (vide pp. 220-221).

PLATE XVI (facing page 222).

Diagram showing the conditions which obtain when, in accordance with Gordon's suggestion, the dimensions of the radiant field are severely restricted. The general scheme of the diagram is the same as that employed in connexion with Plate XIV. To be noted is the circumstance that, in conformity with the fact that the full aperture of the condenser is employed, the radiant points on the stage now furnish beams which fill in the whole apertural plane of the objective (B) furnishing on the now only partially illuminated image plane of the objective (A) the smaller antipoints which correspond to that full aperture (vide pp. 220-221).

PLATE XVII (facing page 224).

Diagram showing the conditions which obtain where the objective is out of allineation with the condenser. The general scheme of the diagram is the same as that employed in Plate XIV. To be noted is the circumstance that, owing to the unsymmetrical manner in which the beams are cut down in the course of their passage through the objective, they are represented in the image plane by ellipitical antipoints (vide p. 222).

PLATE XVIII (facing page 236).

Photographs exhibiting the impediments to microscopic resolution which are referable to diffraction and obfuscation and the improvement which is effected in the highly magnified microscopic image by the employment of Gordon's device for opening up the beam in the image plane of the objective.

Figs. A, B, C are photographs obtained by the aid of Gordon's microphotographic apparatus used in conjunction with his tandem microscope giving upon the photographic plate an actual magnification of circ. 2,500 diameters and a magnification upon the retina that would be conventionally described (vide Cap. X, subsect. 4) as a magnification of about 7,500.

Fig. A. Group of typhoid bacilli imaged by Gordon's tandem microscope employed without the ground glass screen. To be noted are the shadows and diffraction patterns of small particles of dust lying on the eye lens (vide pp. 93-94; pp. 227-228; p. 233 and p. 236). We have here the factor which is contributed by the microscope to the obfuscation and diffraction which mar the highly magnified microscopic image.

Fig. B. Photograph of the central portion of the entoptic picture depicted in Plate X, Fig. 5 (vide pp. 140-142, p. 167, p. 228, p. 233, and p. 237). This represents the factor which is contributed by the eye to the obfuscation and diffraction which mar the highly magnified microscopic image.