434 Wright and Larsen — QaaHz as a Geologic Thermometer. 



Table V. 



Thermoelement of Microscope. 



Temperature of change. 



Quartz- Plate I. 





Freshly drawn thermoelement from standard 

 thermoelement wire. 





Temperature of change. 





Temperature 







Quartz-Plate II. 





of 



Rising. Falling. 









Current in furnace 



change. 















Quartz- Pi»+^ T 



Rate of heating Rate of cooling 





















<D 



<x> 



CD 





CD 



CD 



CD 



Fast 



Slow 



Fast 



Slow 



Rising 





Falling p> [Rising p* 



i 



Falling p» 



Rising p> 



Falling^ 



576 ! 8 



576 ? 7 



574 ? 9 



575 ? 2 



573-7 



f* 



572-7 s 573-4 / 



572 ? 4 



f 



576-4 / 



575-5 s 



576-8 



576-7 



575-0 



575-3 



573-4 



S 



572-7 s 573-6 f 



572-8 



s 



576-5 / 



575-5 s 



576-7 



576-8 



574-8 



575-3 



573-4 



s 



572-6 8 573-5 f 



572-8 



s 



576-1 vs 



575-7 s 



576-5 



576-7 



574-6 



575-2 573-4 



f 



572-6 s 573-4 / 



572-6 



f 



576-1 vs 



575-6 s 



576 7 



576-6 



575-0 



575-2 573-4 



f 



572-4 / 







576-2 s 



575-4 s 



576-7 





5752 







572-5 / 









575-4 / 



5767 





574-9 









572-5 / 











575-4 / 



576-8 





574-9 





















576-7 





574-6 

























574-5 

















576°3 





576 ? 7 



576 ? 7 



574 ? 8 



575 ? 2 573-5 



572 ? 6 



573-5 



572-6 



575*5 



*/, fast ; s, slow. 



Table 5. In this table the results of the determination of the temper- 

 ature of inversion of quartz by means of the abrupt change in its birefring- 

 ence at this temperature are recorded. In the first four columns the read- 

 ings of the ordinary thermal microscope thermal element are given, while 

 in the remaining six the readings on a standard thermoelement of specially 

 thin wire are presented. The point of inversion was recorded both for 

 rising and falling temperatures and different rates of heating and cooling 

 the quartz plates. 



varied slightly with the rate of loss of heat. To insure still 

 further the accuracy of the determination of the temperature 

 of inversion, a new and carefully calibrated thermoelement of 

 line wire drawn down from one of the laboratory standard 

 thermoelements * was taken and the observations in the ther- 

 mal microscope repeated, the readings being taken as before 

 on the potentiometer. The results show again the extreme 

 sensitiveness of quartz to minute temperature differences at 

 the inversion point, and establish the temperature of inversion 

 at 575-8°± 1-0° for the first specimen (Quartz plate 1), 5730° 

 ±0*5° for the second (Quartz plate 2), and 575-9°±0'4 o for 

 the third (Quartz plate 3), or in general for this constant, 575°. 

 ±2°. The results of these observations are recorded in Table 

 5 above. Plate 2 was *232 mm thick and covered an area of 



* It was found necessary to take this precaution and to use wire "2 mm in dia- 

 meter, in place of the standard therornoelement wire 0'6 mm in diameter, 

 since the latter conducts away more heat in unit time than a small furnace 

 can supply, and as a result the readings with it are uncertain and too low. 



