336 



BRIDGMAN 



total effect at 25°. At 50° the e.m.f. is throughout positive, but the 

 direction of cu^^•atul•e is the same as at 25°, wliich allows a maximum 

 at about 6000 kg. The effect at 50° does not at its maximum attain 

 one half the numerical value at 25°, and the hysteresis at 50° is one 

 third the total effect at 50°. At 75° the effect is much larger; the 

 curvature is the same, and the maximum has disappeared. The 

 indications are that there is a maximum at some much higher pressure 



0° 10° 20° 30° 40° 50° 60° 70° 



Temperature 

 Pure Iron Annealed 



Figure 27. American Ingot Iron, Annealed. Thermal E.M.F. of a couple 

 composed of one branch of uncompressed metal, the other compressed to the 

 pressure in kg. cm.- indicated on the curves, the junctions being at 0°C and 

 the temperature plotted as abscissae. 



than 12000 kg. The hysteresis at 75° is 12% of the maximum at 75°. 

 At 75° and 50° the hysteresis is abnormal in direction, being a hasten- 

 ing forward instead of a lagging behind. It should properly not be 

 called a hysteresis at all; and must be due to a flifferent kind of failure 

 of internal equilibrium from the ordinary effect. At 99° the character 

 of the curve is the same as at 75°; the greatest e.m.f. is twice that at 



