Modes of Physical Force. 1 03 



ray pass along the line of magnetic force from the north 

 pole to the south, to the left in the contrary case ; or if 

 the substance through which the ray be transmitted be, 

 like turpentine, itself capable of deflecting the plane of 

 polarization, then the magnetism, according to its 

 direction, increases or diminishes this rotation. Material 

 change in connexion with magnetism is also made 

 evident in the altered dimensions of a bar of iron in 

 passing to or from the magnetic state, as well as in the 

 loss of magnetism which is caused by beating or twist- 

 ing or heating a magnetized rod of steel ; and there are 

 other facts which seem to show that this material 

 change has in it something of chemical nature. One of 

 these may be found by seeking for it in the composition 

 of magnetic oxide of iron, for here is a substance which 

 is apparently magnetic because in it two oxides are 

 mixed together in certain proportions. The magnetic 

 oxide is made by mixing the two non-magnetic oxides, 

 and, therefore, this fact may not suffice to connect 

 magnetism with material changes of a chemical nature : 

 and certainly it does not do this so closely as a fact 

 supplied in an experiment of which this account is 

 given by Grove. " If a battery of one cell, just capable 

 of decomposing water and no more, be employed, this 

 will cease to decompose while making a magnet. There 

 must, in every case, be preponderating chemical 

 affinity in the battery cells, either by the nature of 

 its elements or by the reduplication in series, to effect 

 decomposition in the voltameter j and if the point is 

 just reached at which this is effected, and the power is 

 then reduced by any resistance, decomposition ceases ; 

 were it otherwise, were the decomposition in the volta- 

 meter the exponent of the entire force of the generating 

 cells, and these could independently produce magnetic 



