WRIGHT: CHANGE IN ANGLES OF QUARTZ 



489 



TABLE 1— Continued 



Note: In this table the different sets of readings are lettered thus: a readings 

 made on October 4; 6, on October 7; c, on October 8; d, on October 10; e, on 

 October 15; /, on October 17; g, on October 18; li, on October 22; i, on October 24; 

 fc, on October 27; /, on October 28, 1913. All crystals measured were from Herki- 

 mer Co., N. Y., and were kindly loaned to the Laboratory by the U. S. National 

 Museum (Specimen No. 82925). 



In Table 1 the computed changes in the polar angle p for the unit 

 rhombohedi'on (1011) are given in place of the measured angles, 

 which of themselves have no direct significance because the crys- 

 tals were purposely not accurately adjusted before the measure- 

 ment. 



The heavy curve in figure 1 represents the average value of the 

 observations. At 575° it has a noticeable discontinuity which 

 marks the transformation of a into /3 quartz; this is accompanied 

 by a noticeable change in volume and also in the optical and crys- 

 tallographical properties. At the inversion temperature the 

 reflexion signals from all of the faces, both rhombohedi'on and 

 prism, become temporarily (2 to 5 seconds) indistinct; the sharp 

 signal widens out into a hazy patch of light, moves noticeably and 



