Illumination with Plane Mirror. By Dr. H. E. Fripp. 745 



mirror (Fig. 67, 1 p,7 p), touch the object by their outside ray only, 

 the remainder passing by on either side. And, further, that a 

 parallel beam incident also upon the whole mirror surface, but at 

 right angles to the axis of the Microscope, illumines the object by 



Fig. 67. 



l^p, two rays drawn parallel with 1 and 7 respectively. The parallel beams 

 1 p and p 7 occupy the mirror surface, but instead of being reflected on the 

 object, fall outside of it, excepting the rays 1 and 7. 



. its axial ray alone, as shown in Fig. 68. So also if each of the inter- 

 vening lines (2, 3, 4, 5, 6, Fig. 66) represented the course of as 

 many parallel beams occupying the whole mirror surface with the 



Fir,. G8. 



Piinillcl beam incident on minor at anu'lo of 4;") " to axis of Microscope. Its 

 axi;il ray alone fall.s on tlie object. Witli dilfereiit inclination the central ray 

 falls away fnim the; oljjict, and the illnminaliun becomes obliinio: namely, from 

 some point of mirror snrfaee more or less distant from its centre. This oldiiiuity 

 of direction does not indicate convergence of light, as it comes from one side 

 only at a time. 



incidence belonging to each line respectively, it is manifest that 

 the rays would fall on dilfcrent surface elements of the mirror, and 



