THERMO-ELECTRIC QUALITY I'NDER PRESSURE. 



273 



Such a couple involves both temperature and stress gradients. 

 The stress gradient is rendered ineffective by keeping the regions in 

 which there is such a gradient at constant temperature. Thermo- 

 dynamics shows that no closed circuit of the same or different metals 

 under different or Aarying stresses can possibly be the seat of an e.m.f. 

 if the whole is at one constant temperature. If, then, all regions of 



Figure 1. The electrical connections in place in the pressure cylinders. 



varying temperature in a complete circuit are regions of no stress 

 gradient, we are sure that stress gradients in other parts of the circuit 

 can produce no resultant e.m.f. around the circuit. 



The part of the apparatus concerned in the thermal e.m.f. measure- 

 ments consists of two heavy cylinders connected by a heavy tube. 

 The two cylinders are maintained at any requ^ired difference of tem- 



