CONCLUDING KEMAEKS. 185 



treating of physical phenomena, will, I think, be evident from 

 the previous parts of this essay, to be that of a necessary 

 reciprocal production : in other words, that any force capable 

 of producing another may, in its turn, be produced by it 

 nay, more, can be itself resisted by the force it produces, in 

 proportion to the energy of such production, as action is ever 

 accompanied and resisted by reaction : thus, the action of an 

 electro-magnetic machine is reacted upon by the magneto- 

 electricity developed by its action. 



To many, however, of the cases we have been consider- 

 ing, the term correlation may be applied in a more strict 

 accordance with its original sense : thus, with regard to the 

 forces of electricity and magnetism in a dynamic state, we 

 cannot electrise a substance without magnetising it we can- 

 not magnetise it without electrising it : each molecule, the 

 instant it is affected by one of these forces, is affected by the 

 other ; but, in transverse directions, the forces are insepara- 

 ble and mutually dependent correlative, but not identical. 



The evolution of one force or mode of force into another 

 has induced many to regard all the different natural agencies 

 as reducible to unity, and as resulting from one force which 

 is the efficient cause of all the others : thus, one author writes 

 to prove that electricity is the cause of every change in 

 matter ; another, that chemical action is the cause of every- 

 thing ; another, that heat is the universal cause, and so on. 

 If, as I have stated it, the true expression of the fact is, that 

 each mode of force is capable of producing the others, and 

 that none of them can be produced but by some other as an 

 anterior force, then any view which regards either of them as 

 abstractedly the efficient cause of all the rest, is erroneous ; 

 the view has, I believe, arisen from a confusion between the 

 abstract or generalised meaning of the term cause, and its 

 concrete or special sense ; the word itself being indiscrimi- 

 nately used in both these senses. 



Another confusion of terms has arisen, and has, indeed, 



