256 



LETTERS ON NATURAL MAGIC. 



If, in place of a solid plate, we strew the sand over a 

 stretched membrane, the sand will form itself into figures, 

 even when the vibrations are communicated to the 

 membrane through the air. In order to make these 

 experiments, we must stretch a thin sheet of wet paper, 

 such as vegetable paper, over the mouth of a tumbler 

 glass with a footstalk, and fix it to the edges with glue. 

 When the paper is dry, a thin layer of dry sand is strewed 

 upon its surface. If we place this membrane upon a 



No. 1. 



Fig. 46. 



No. 2. 



No. 3. 



No. 4. 



table, and hold immediately above it, and parallel to the 

 membrane, a plate of glass vibrating so as to give any of 

 the figures shown in Fig. 46, the sand upon the membrane 

 will imitate exactly the figure upon the glass. If the 

 glass plate, in place of vibrating horizontally, is made to 

 vibrate in an inclined position, the figures on the mem- 

 brane will change with the inclination, and the sand will 

 assume the most curious arrangements. The figures thus 

 produced vary with the size of the membrane, with its 

 material, its tension, and its shape. When the same 



