280 Wenrioh — .1 Study of the Time Interval in a 



Table III (for Curve IV, Fig. 8). 







Time in sec. 



Current 





Heater 



for 2 cm. 



in the heater in 



irtings 



setting in cm. 



defl. 



milliamperes 



1 



2~rbo 



- - _ - 



118-5 



2 



28-00 



154-4 



118-2 



3 



28-10 



102-0 



119-5 



4 



28-30 



62-8 



119-4 



5 



28-50 



45-0 



119-2 



6 



29-00 



30-3 



119-1 



1 



29-50 



25-5 



119-3 



8 



30-00 



21-4 



119-6 



9 



30-50 



18-8 



120-2 



10 



31-00 



16-5 



120-0 



11 



31-50 



16-0 



1193 



12 



32-00 



15-0 



119-5 



13 



32-50 



14-0 



119-5 



14 



33-00 



140 



119-2 



15 



33-50 



13-9 



119-8 



the wires, which are also shown. by the full lines in figure 4. 

 The battery B was now abandoned and the heater, joined in 

 series with a variable resistance, connected across a 110- volt 

 circuit. For different setting? or positions of the heater over 

 one arm of the bridge, curves were plotted connecting the cur- 

 rent in the heater with the time for deflecting the galva- 

 nometer coil a certain number of divisions. See figure 8 for 

 these curves and Tables III and IV for the data. For all 

 these curves, the bridge current was very constant at - l 

 ampere. Curve IV connects the time with different settings of 

 the heater along one arm of the bridge. The curve is parallel 

 to the X-axis for the last three points or settings. These were 

 positions when the heater was off one arm and only moving 

 over the other. As seen in Table III, the heating current for 

 this curve was nearly constant. 



It was interesting to note that the electrical center for the 

 heater, i. e., the position of symmetry, was only three milli- 

 meters away from the measured center. 



It was noticed that there was a considerable time lag in the 

 starting of the galvanometer coil after the heater switch was 

 closed. In Table IV, for curve III, this lag is recorded. 



This lag seems to indicate that the glass tube absorbed the 

 radiation from the heater, thereby raising its temperature. 

 This would lessen the radiation from the arm in the tube and 

 hence raise its temperature. The change of resistance in the 

 arm effected in this way gave rise to current in the 

 galvanometer. This means that the current in the gal- 

 vanometer is a function of the difference of temperature 



