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Proceedings of the Royal Society of Edinburgh. [Sess. 
6. Extra-fine ground glass, ground side towards light. Photomicrograph, Plate I. fig. 3. 
7. The same, but ground side away from light. ,, Plate I. fig. 3. 
8. Ground glass etched by acid, ground side towards light. ,, Plate I. fig. 4, 
and Plate II. fig. 5. 
Angle at which the incident beam of light falls on the plate. 
Fig. 5. 
11. Extra-fine ground glass, ground side towards light, normal emission and oblique incidence. 
12. The same, but ground side away from light. Photomicrograph, Plate I. fig. 3. 
18. A repetition of 11, some time later after readjustments. 
Curves of relative intensity. Curves of maximum total emission. 
