34 N. N. ZIRBEL 
tion was reached in about 7 hours instead of many days. At higher tempera- 
tures still less time was required. During this baking process the total rota- 
tion was often 180° or more. It was also found that if a wire from which the 
time drift had been removed by baking were strained beyond the elastic 
limit by a longitudinal stress, then the time drift again appeared and could 
Mat Pt+OZir 
Diameter 0.04mm 
Length 50cm 
Loa 20gm 
Scale Dist. |\2Ocm 
Temp Coef -08: C 

Fig. 1. 
be removed only by further baking. The same result followed when the brass 
cylinder attached to the lower end of the wire was twisted through about 
half a revolution and held in this twisted position for several hours. 
The time drift is thus quite easily removed. There remains, however, the 
change in equilibrium position with the temperature of the wire, as shown 
in Fig. 1. 
The next problem is then to study the effect of heat treatment on this 
temperature coefficient, which in Fig. 1 is —0.08 mm per °C. Fig. 2 shows 
Ny] p205 ° 
o 


J wu 
Material Pt+lOZir 
Diameter O0O4mm 
Length 50cm 
Load 20gm 
Scale Dist !12Ocm 
0 Oe 



Fig. 2. 
the results of such a study. The complete procedure in obtaining these re- 
sults is as follows. The wire is hung up with a load of 20 grams and baked 
at 230°C for 6 hours. This baking removes the time drift. The temperature 
coefficient is then obtained by taking the readings shown in Fig. 1 and is 
found to be —0.08 mm per °C. This value gives the first point on Fig. 2. The 
178 
