204 Dr. Tyudall on t%e Progress of the Physical Sciences, 



It will not be necessary to give tlie full tabular statement of 

 the experiments which Buff and Zamminer have made with their 

 thickest magnet^ as the pith of the controversy lies in the results 

 given in the last table. It willj however, be interesting to know 



how the quotients ^ agree among themselves, and what 



^ tan 9 



agreement exists between the observed and calculated values of yjr. 

 Bar No. 4. 



In the first seven of these experiments the power applied was 

 very great ; it varied from 82'^-25 to 59°. The power in the last 

 seven experiments varied from 60° to 9°. In the former case 

 the full current was not allowed to pass round the tangent needle, 

 but a branch current about the 19th part of the full one. 



The observed values of ijlr are found by subtracting tan <f>" 

 from tan (}>, and ascertaining the corresponding angle in table 

 of tangents. The calculated values of yjr are derived on the 



The inconsider- 



+ 0-1-1 *w^ 



assumption that t— T- is a constant quantity. 



able, or at least irregular, differences between the observed and 

 calculated values of ^jr justify this assumption, and establish the 

 law of Lenz and Jacobi, at least in those cases where the core 

 consists of good soft iron. 



^Vhence, then, (demand Buff and Zamminer) those remark- 

 able divergences which have been observed by Miiller ? It is 

 hardly possible to account for them satisfactorily so long as the 

 details of his experiments, which are omitted in his memoir, 

 remain undescribed. We believe, however, that we are justified 

 in the conjecture, that the ground thereof lies partly in the defect 



