CHAPTER VII 



ILLUMINATION 



Methods of Illumination. — There are five chief methods 

 of microscope illumination, which, when tried by Hart- 

 ridge (71), yielded satisfactory results, with corrected 

 lenses. These are: (1) focusing the original incandescent 



Fig. 16. — Diagram showing the aperture circles in the microscope, dependinjr 

 on the aperture of the objective and the used aperture of the condenser. A point 

 on the center of the source of hght (which is a ground glass circle equal to the 

 source-field .Si, bounded by a diaphragm, and illuminated by the lamp L) sends 

 a cone of rays through the color screen, to be reflected by the prism, and fill the 

 opening C\ of the condenser. This cone is condensed on the center of the object- 

 field .S'>; whence it passes to partly fill the aperture circle of the objective 0\, 

 as the condenser aperture circle C'2. These circles are imaged and focused by 

 the eyepiece at the eyepoint, forming the eyepiece circles O2 and C'3, from which 

 pencils of parallel rays pass to the eye. 



source on the object; (2) using hght from ground glass, 

 which is like cloud light; (3) using a corrected bull's eye 

 to magnify a small source, and then focusing the magnified 

 image on the object; (4) making the rays parallel with a 



66 



