174 Prof. Tyndall on the Nature of the Force by which 



Table VI. 



Bar of compressed carbonate of irou. 



Length 0*95 of an inch; width 0'17 of an inch ; depth 0*23 



It is needless to remark upon the perfect similarity of deport- 

 ment here exhibited to the cases previously recorded. 



In the following instances the same law of increase is obser- 

 vable. 



Table' VII. 



Sulphate of iron, No. 1. 

 length 0'75 of an inch, 

 width 0"22 of an inch, 

 depth 0*27 of an inch. 



Set axial between the excited 

 poles. 



Sti'ength of current. 

 71 

 182 

 217 

 280 

 328 

 359 



Attraction. 

 702 

 1332 

 2202 

 2752 

 3332 

 3482 



Table VIII. 



Sulphate of iron, No. 2. 

 length 0'75 of an inch, 

 width 0'22 of an inch, 

 depth 0"27 of an inch. 



Set equatorial between the ex- 

 cited poles. 



Strength of current. 

 70 

 121 

 203 

 271 

 331 

 370 



Attraction. 

 682 

 1232 

 2072 

 2682 

 3082 

 3342 



In sulphate of iron there is one direction, which, in virtue of 

 the molecular structure of the substance, sets strongly from pole 

 to pole. The bar No. 1 was so cut that this direction was 

 parallel to its length, which therefore set axial ; while No. 2 had 

 the same direction across it, thus causing the length of the bar 

 to set equatorial. 



Two comparative series were finally made with two prisms of 



