LAW OF CAUSATION. 251 



whom we can suppose acquainted with the original distribution of all nat- 

 ural agents, and with the whole of their properties, that is, the laws of suc- 

 cession existing between them and their effects : saving the far more than 

 imman powers of combination and calculation which would be required, 

 even in one possessing the data, for the actual performance of the task. 



§ 9. Since every thing which occurs is determined by laws of causation 

 and collocations of the original causes, it follows that the co-existences 

 which are observable among effects can not be themselves the subject of 

 any similar set of laws, distinct from laws of causation. Uniformities 

 there are, as well of co-existence as of succession, among effects ; but these 

 must in all cases be a mere result either of the identity or of the co-exist- 

 ence of their causes : if the causes did not co-exist, neither could the ef- 

 fects. And these causes being also effects of prior causes, and these of 

 others, until we reach the primeval causes, it follows that (except in the 

 case of effects which can be traced immediately or remotely to one and 

 the same cause) the co-existences of phenomena can in no case be univers- 

 al, unless the co-existences of the primeval causes to which the effects are 

 ultimately traceable can be reduced to a universal law : but we have seen 

 that they can not. There are, accordingly, no original and independent, in 

 other words no unconditional, uniformities of co-existence, between effects 

 of different causes ; if they co-exist, it is only because the causes have cas- 

 ually co-existed. The only independent and unconditional co - existences 

 which are sufficiently invariable to have any claim to the character of 

 laws, are between different and mutually independent effects of the same 

 cause; in other words, between different properties of the same natural 

 agent. This portion of the Laws of Nature will be treated of in the lat- 

 ter part of the present Book, under the name of the Specific Properties of 

 Kinds, 



§ 10. Since the first publication of the present treatise, the sciences of 

 physical nature have made a great advance in generalization, through the 

 doctrine known as the Conservation or Persistence of Force. This impo- 

 sing edifice of theory, the building and laying out of which has for some 

 time been the principal occupation of the most systematic minds among 

 physical inquirers, consists of two stages : one, of ascertained fact, the oth- 

 er containing a large element of hypothesis. 



To begin with the first. It is proved by numerous facts, both natural 

 and of artificial production, that agencies which had been regarded as dis- 

 tinct and independent sources of force — heat, electricity, chemical action, 

 nervous and muscular action, momentum of moving bodies — are inter- 

 changeable, in definite and fixed quantities, with one another. It had long 

 been known that these dissimilar phenomena had the power, under certain 

 conditions, of producing one another : what is new in the theory is a more 

 accurate estimation of what this production consists in. What happens is, 

 that the whole or part of the one kind of phenomena disappears, and is re- 

 placed by phenomena of one of the other descriptions, and that there is an 

 equivalence in quantity between the phenomena that have disappeared and 

 those which have been produced, insomuch that if the process be reversed, 

 the very same quantity which had disappeared will re-appear, without in- 

 crease or diminution. Thus the amount of heat which will raise the tem- 

 perature of a pound of water one degree of the thei-mometer, will, if ex- 

 pended, say in the expansion of steam, lift a weight of 772 pounds one 



