and Crystals of Quartz loith hydrofluoric acid. 161 



After leaving the sphere in the acid for a few hours, the etchings 

 were distinctly observed and their arrangement on the sphere was 

 such that its crystalline nature and relation to hexagonal axes could 

 be determined. The location of the extremities of the vertical axis 

 was marked by the centers of two triangular patches on opposite 

 sides of the sphere, while tlie character and arrangement of the 

 prominent etchings on the positive rhombohedron indicated the right 

 handed character of the crystal from which the sphere was cut as 

 well as tlie location of the extremities of the lateral axes. After 

 being in the acid for about four days some of the etchings were very 

 prominent, and the spliere had the appearance represented in figures 

 1 and 2, plate II. In figure 1 we are looking down upon the sphere 

 in the direction of the vertical axis. In the centre there is a distinct, 

 somewhat hexagonal field, the center of whicli marks the extremity 

 of the vertical axis. This whole portion is one where the etching 

 has gone on very vigorously, and with the microscope it can be seen 

 that the surface is composed of minute triangular pyramids grouped 

 closely together. About this, three prominent parts, which are ar- 

 ranged in the alternating sections of the hexagon, indicate the 

 position of the positive rhombohedron by the greater extent of the 

 etching, leaving very distinct prominences with their steep sides 

 turned to the right. A distinct ridge or marking, from which the 

 lines of etching go ofl" very distinctly, can also be seen about in the 

 center of each negative rhombohedron. In fig. 2, we are looking at 

 the sphere about at right angles to a prismatic face. A little above 

 the center of the figure and trending to the right, the prominent 

 etchings, indicating the position of the positive rhombohedron, can 

 be seen, while below and to the right they can also be seen in the 

 position of the lower positive rhombohedron. On what may be 

 called the equator of the sphere, midway between the above men- 

 tioned prominent etchings on the positive rhombohedrons above and 

 below, the extremity of one of the lateral axes can be located a little 

 to the right of the center of the figure. On much of the surface near 

 the equator of the sphere, the original polish has not been destroyed. 

 The vigorous action of the acid at the extremities of the vertical axis 

 is plainly seen accompanied already by a slight flattening of the 

 sphere. 



After exposing the sphere again to the action of the acid for about 

 two weeks it had the appearance represented in figures '6 and 4, plate 

 11, In figure 3, where we are looking down upon the sphere in the 

 direction of the vertical axis, three parts on the equator, located by 



