524 



IOWA ACADEMY OF. SCIENCE Vol. XXVI, 1919 



FIGURE 130 



whole into evacuated glass tubes. They were then subjected to tem- 

 peratures varying from — 79 degrees C. to +280 degrees C. No 

 maximum was found. Curves are given for three such crystals. 

 The curve obtained by Tisdale- is also included for comparison. The 

 maximum effect is probably due to the heating produced by the cur- 

 rent used in the method of measurement. 



'Loc. cit. State University of Iowa. 



