162 Meyer and Penfield — Results obtained hy Etching a Sphere 



the right hand and upper and lower left hand angles of the hexagon, 

 indicate one extremity of each of the three lateral axes and from 

 these parts the lines of etching run out very beautifully toward the 

 center and the prominent marking on the rhombohedron faces. In 

 figure 4, where we are looking at right angles to the vertical axis, 

 besides the decided flattening, a rhombic portion, about in the center 

 of the field, is conspicuous, the center of which locates the extremity 

 of one of the lateral axes. On this portion not only could the origi- 

 nal curved surface of the sphere be detected but also the original 

 polish. The acid having had apparently no action on this portion 

 of the sphere, while the etched portions come up to meet this with 

 sharp and distinct angles. Owing to a slight misunderstanding a 

 mistake was made in photographing figure 4, which was not discov- 

 ered till it was too late to correct it. If we imagine the sphere 

 turned 90° so that the unattacked portion would appear at the right 

 and seen at a tangent, while one of the two similar portions which 

 are now behind and out of sight would appear in the front and a 

 little to the left, the quartz would appear in just the right position 

 to compare with figures 2 and 6. As it is we are looking at the 

 crystal not at right angles to a prism in but at right angles to a prism 

 of the second order I2l0. 



By exposing the quartz for about one month longer to the action 

 of the acid it appeared as represented in figures 5 and 6, plate II. In 

 figure 5, which is again a vertical view, we can readily locate the ex- 

 tremities of the three lateral axes by the right hand and upper and 

 lower left hand angles of the hexagon. At these parts the curved 

 contour of the sphere is preserved for a short distance, but between 

 them there is a decided tendency toward a triangular cross section. 

 The sphere as will be seen from figure 6 has become extremely flat- 

 tened and the upper and lower portions meet along a very sharply 

 defined line. The etchings seem to arrange themselves along parallel 

 lines or ridges and some idea of their beautiful arrangement can be 

 obtained from the larger reproduction shown in figure 3, plate I. In 

 figure 6 we notice, in addition to the extreme flattening, two of the 

 three portions where the acid has had very little action, one taken at 

 a tangent to the right, the other a little to the left of the center ; 

 these appear as very conspicuous parallelograms ; they have a 

 curved surface similar to that of the original sphere, and although 

 the original polish has disappeared from them only the finest etchings 

 can be detected with the microscope. It can almost be said that the 

 acid has had no action on these three surfaces, at least not enough to 



