and Crystals of Quartz toith hydrofluoric acid. 165 



EXPLANATION OF PLATES. 



Plate I. 



1. Etchings produced ou the faces of a right handed quartz crystal by hydrofluoric 

 acid. 



2. Etchings produced on the faces of a left handed quartz crystal by hydrofluoric 

 acid. 



3. Final result of eating away the greater part of a sphere (cut from a right handed 

 quartz crystal) with hydrofluoric acid during a period of about eight weeks. Seen in 

 the direction of the vertical axis. Tiie angles of the hexagon mark the extremities of 

 the lateral axes. 



Plate fl. 



'1 and 2. Appearance of the etched sphere after being in the acid about four days. 

 1. Seen in the direction of the vertical axis. 2. Seen in the direction at right angles 

 to the vertical axis and a prism of the first order. 



3 and 4. Appearance of the etched sphere after being in the acid about three 

 weeks. 3. Seen as in 1. 4. Owing to a mistake in taking the photograph seen about 

 at right angles to a prism of the second order. 



5 and 6. Appearance of the etched sphere after being in the acid about seven 

 weeks. 5. Seen as in 1 and 3. 6. Seen as in 2. 



Trans. Conn. Acad., Vol. VIIT. 22 Dec, 1889. 



