[BARNES] EFFECT OF STRAIN ON THE EXPANSION OF QUARTZ 149 



rotates with a steel roller supporting the quartz tube. The steel roller 

 is held on plate glass resting on a portion of the supporting base B. 



Since the object of the experiments was to compare the expansion 

 of the tube when under different tensions, and to find out whether any 

 effect was present, no effort was made to determine the coefficient of 

 expansion in absolute measure. 



Had an effect existed, more refined measurements would have 

 been undertaken. The temperature interval was taken between the 

 temperature of the room and that of steam supplied by an ordinary 

 boiler. Different weights were used on the scale pan up to the breaking 

 strength of the quartz tube. 



The following table contains the result of the tests. The de- 

 flection represents the change in scale reading observed in the telescope 

 which was placed about two meters away from the mirror. 



Air Temp. Steam. Weight. Deflection. 



20-5°C 100°C 1 kilo 7-65 Cms. 



20-5 100 2 kilos 7-19 



20-5 100 7-2 kilos 7-17 



20-5 100 8 kilos 7-00 



20-8 100 1 kilo 7-65 



20-8 100 1 kilo 7-13 

 Above 8 kilos tube failed. 



<An approximate calculation of the coefficient of expansion rep- 

 resented by a movement of the quartz tube necessary to give a de- 

 flection of 7 centimetres on the scale, gave a result in very good agree- 

 ment with the best values for this temperature interval i.e., 0-4X10"^ 

 cm. 



It is evident that no effect of strain is observable in these experi- 

 ments greater than the probable error of observation. It will be 

 necessary to seek the cause of the discrepancy elsewhere. 



