Fic. 160.—The same etch pits in CAB as in Figure 159 except that the focal plane of the microscope is nowslightly below the plastic surface, Slight changes in focus are an aid in distinguishing etch pits from imperfections.
Fic. 160.—The same etch pits in CAB as in Figure 159 except that the focal plane of the microscope is nowslightly below the plastic surface, Slight changes in focus are an aid in distinguishing etch pits from imperfections.