140 Mr. Charles Tomlinson, on the Curved Figures 



axial end of the slit, is either at or exterior to the edge of 

 the disk, according to the position of the eye. 



This figure (2 b) is produced when the slit cuts the striae 

 at right angles, but when it is parallel to them the figure 

 is totally changed : the bands are all rectilinear, but their 

 parallism is destroyed, as they all seem to diverge from a 

 point situate at the axial end of the slit. Again, when the 

 slit is inclined 45° to the striae, the image presents the 

 shell-like form represented in 



Fig. 2 c. 



The same principle, but beautifully modified in its appli- 

 cation, is perceptible on employing a chequered disk. 



Fi-. 3. 



The figure which illustrates the striated disk, when 

 simply revolving, figure 2 a, will apply to the present, 

 the only difterence being a more gentle blending of the an- 

 nular tints into each other ; but when viewed through the 

 slit, the reflected image presents the appearance of a tes- 

 selated globe, and the illusion is so perfect that it requires 

 an effort to preserve the idea of a flat surface. Figure 3 a. 



