WRIGHT: CHANGE IN ANGLES OF QUARTZ 



487 



From the position angles of the faces thus measured the angles 

 between the unit rhombohedrons over the pole were computed; 

 also the angle between the unit rhombohedron and the prism face 

 immediately below it. 



During the measurements the adjustment of the goniometer 

 was tested and found satisfactory. Readings were made to j of 

 arc, the circle being graduated to ^'.^ j^^ h^q j^igj^ temperatures 

 the light from the furnace itself is so intense that an arc light is re- 



51-30 



35 



5140 



45 



51 50 



O 500 1000° 



Fig. 1 



quired for illuminating the signal. The Hght of the furnace was 

 cut out to a large extent by means of a blue filter (Wratten tri- 

 color blue) which absorbed all of the red and yellow and most of 

 the green of the spectrum, colors which are most intense in the 

 furnace, whereas the arc light emits relatively more blue light. 

 At 1250° the signals observed thru this filter were perfectly 

 sharp and the measurements were as easy to make as at room 

 temperatures. 



The results of measurements are listed in Table 1 and are rep- 

 resented graphically in figure 1. / 



2 In making the readings the quarters of minutes were recorded as follows : 

 /^' = 1-; 3^' = 1'; M' = 1' ; this method of indicating the quarter minutes was 

 found convenient and satisfactory' in practice. 



