THE AID OF THE ACHROMATIC FRINGES. 



31 



Similarly, the data for Swedish iron in the next paragraph if treated in the 

 same way, give k=i.g, 1.5, 1.4, in fields of 500, 700, 800 gauss, respectively. 

 The assumption of a mean susceptibility of this order, which seems more than 

 given by the behavior of iron, would suffice to account for the observed 

 contractions. 



Hence the estimate of susceptibility obtainable in this way, though treated 

 as a constant, is not of a wholly unreasonable order of mean value. The 

 curve of equation (3) can not, of course, conform with the data of figure 32; 



8 



for k is essentially variable and an initial length free from the initial 

 complications must be assumed. Further inquiry will be made in the 

 next paragraph. 



18. Further observations. As there is something objectionable in a result 

 pieced together out of separate observations, the data of table 3 and figure 33 

 were investigated in a single series. To reduce the heat discrepancy a brisk 

 current of water was passed through the tubular water-jacket. This seemed 

 the safer plan, even though the fringes were shaken. The observations were 

 made in triplets and largely confined to the higher fields. 



