HALL AND CAMPBELL. — MAGNETIC EFFECTS IN SOFT IRON. 653 



(VI.) 

 100° 1171 200° 771 



With these vahies of ^S* the iron line of Figure 1 2 has been plotted. 

 Various points of the copper line have been found by measuring to the 

 left from the corresponding points of the iron line distances represent- 

 ing the thermo-electric heights of iron with respect to copper at the 

 various temperatures. The iron line is decidedly concave toward the 

 left, the copper line, according to our data, has a much smaller incli- 

 nation from the vertical than the iron line, indicating a much smaller 

 Thomson effect in copper than in iron, and is slightly concave toward 

 the right. 



If we now, taking our values of ^S* for certain temperatures, e. g. 20°, 

 40°, 60°, 80°, 100°, test the Voigt formula for these temperatures, we 

 find. 



Comparison of this table with Table II. will show that the Voigt 

 formula, with the value of — aS* (or ©') found as we have found it, agrees 

 with our data considerably better than the Moreau formula does. Each 

 formula is right in our case as to signs ^^ and each is satisfied by our data 

 at some one temperature, which is near 80° C. for the Moreau formula 

 and not very many degrees higher for the Voigt formula. Above the 

 temperature of agreement ^ Te is too small for the Moreau formula and 

 too large for the Voigt formula. It is to be remembered that neither 

 eTg nor f,Te has been determined very accurately, nor is the temper- 

 ature-coefficient of either precisely known. It seems to us, however, 

 very unlikely that our errors of measurement are great enough to 

 account for the disagreement between either formula and our data. It 

 is probable that neither formula is correct. 



^^ There may be some doubt as to the signs. See the Postscript to this 

 paper. 



