align="right" valign="top">68.

For demonstrating retiring and advancing colors 137 69. By combining these stereoscopically the effect of metallic lustre (similar to graphite in this case) is obtained 141 70. A bas-relief lighted from above 146 71. An intaglio lighted from above 147 72. A bas-relief lighted from the left 148 73. An intaglio lighted from the left 149 74a. A disk (above) and a sphere (below) lighted from overhead 145 b. A disk and a sphere lighted by perfectly diffused light 145 75. A concave hemispherical cup on the left and a convex hemisphere on the right lighted by a light-source of large angle such as a window 150 76. The same as Fig. 75, but lighted by a very small light-source 151 77. Apparent ending of a searchlight beam 161 78. An accurate tracing from a photograph (continual exposure) of the moon rising 171 79. Accurate tracings from a photograph (short exposures at intervals) of the sun setting 172 80. Explanation offered by Smith of the apparent enlargement of heavenly bodies near the horizon 174 81. Explanation of a common mirage 176 82. Illustrating the apparent distortion of a picture frame in which the grain of the wood is visible 190 83. Another example similar to Fig. 82 191 84. From actual photographs of the end-grain of a board