ABSTRACT
When light passes through a small piece of transparent solid immersed in a liquid having a lower RI, it bends toward the solid. As light passes through a small piece of transparent solid immersed in a liquid having a higher RI, it bends toward the liquid (Figure 3.3). If white or polychromatic light is used to illuminate a solid, a BL in the shape of a bright white halo forms when the focus is raised. The movement of the BL is then used to determine whether the solid or MTM has the higher RI. Remember, when the focus of a 10
×
objective is raised after being sharply focused on a specimen, the BL always moves toward the medium of higher RI. Figures 3.3 and 3.4 illustrate BL development and movement. The BL is shown as a bright white halo moving toward the particle (Figure 3.4, left). The BL is a bright white halo moving toward the MTM (Figure 3.4, right). The solid in the center section is in sharp focus and exhibits no BL.
