These form Class 3. Remembering the old rule, that 

 the thermo-clcctromotivc force is proportional to the d 

 cncc of temperature of the junctions, let us construct s<mr 

 couples, 5% x % x ft inches, by taking 18 gauge 

 iron, and cutting the ends into three slits, which, \\lun 

 twisted and having the ZA poured in, will form the junctions 

 (sec Fig. 12). Heat up to 375 I-*., and we have only 33 on 

 the galvr. This is clearly going backwards. Now let us try 

 half the length of couple, say ij^ x ^ x #j inches 

 from 20 gauge sheet Iron (Fig. 13), connect up, and at 



Fiy. 13 



the same temperature we have 42 galvr., or a little better 

 than the result of the longer ones (Fig. 12), which is in 

 direct contradiction to the recognized laws on the subject. 



Now let us take wire gauze double, instead of 20 gauge 

 sheet iron, say about 16 mesh, and construct 2 couples, say 

 i l /2 x % x #j inches (Fig. 14). Try them at 410 F., 

 and we get 49 to 50 galvr. This is better. But we will try 



