rklNCIPLES OF GENERAL PHYSIOLOGY 



Fiu. 8. REAL IMAGE OF ONE OF THK SECTIONS OF 

 ABBE'S DIFFRACTION PLATE. Photographed 

 with Leitz j^-iu. oil immersion, projection 

 oc. 4, Powell and Lealaud condenser, full 

 aperture of iris. 



FlU. 9. FOUR DIFFRACTION IMAOES OF THE SAME PART OF THE PLATE AS FIG. 8. 



Photographed with narrow illuminating cone. The images M-ere taken first 

 with Zeiss 16 mm. apochromatic lens, projection oo. 4. No condenser, 

 plane mirror, iris aperture about 0'75 mm. The negatives were then 

 enlarged to the same magnification as the real image in preceding figure, 

 that is, 370 diam. Each division of the scale corresponds to 26 /t- The series 

 of images were obtained by raising the objective through the space between 

 real focus and one-third of a millimetre above. The lower right-hand 

 image is that at the highest position (one-third of a millimetre) above the 

 focus. 



