29 



it must follow that when a small quantity appears to influence the 

 whole of a large one, there must be some deception in the cas 

 which it is proper to examine. 



56. The relation of place between substances is one, the full 

 efficacy of which I will not attempt to define; rather because it 

 would be long and superfluous than because it would be difficult. 

 However, to sketch the leading points of this relation, it may be 

 observed that when things conspire to produce an effect, the 

 agents, though mutually influential, occupy various degrees of 

 intimacy in their combination. The loosest relation of this de- 

 scription is that of the mechanical kind, where the parts preserve 

 their identity without intermixture of particles, and may respec- 

 tively be contemplated independently of the whole, as the parts 

 of a house, a table, an animal, &c. Next to these grosser 

 mechanical instances come those of mixture, where the parts are 

 mingled together in minuter proportions, but still not so intimately 

 as to prevent the separate recognition of different components; 

 as, for example, in an imperfect mixture of powders of different 

 colour and sensible properties. The third example is that of 

 combination, where the intermixture is not by recognizable parts, 

 but between the infinitely, or, to speak more cautiously, the in- 

 visibly subdivided particles. In this last class of the relation of 

 place, all traces of separate components are lost, and the thing 

 appears altogether of one nature, as in the instances of chymical 

 union. 



57. Now this relation of place between agents is settled as 

 before explained by the causes which belong to the agents, they 

 being various and producing the varieties of the relation. But to 

 return to the present topic: the tendency, in the state of combina- 

 tion, of the minutest possible divisions of particles is to separate 

 from the aggregate which they before constituted, and to diffuse 

 themselves to an extent corresponding with their divisibility, and 

 the relation subsisting between their particles, and those of the 

 agent with which they are combined. 



58. In this manner, to recur to our former example, our drop 

 of oil of vitriol, if divided into 7,680 minuter portions, would fur- 

 nish one to each drop in the pint of water: and if this division 

 were again subdivided, one portion to each half drop of the water; 

 in this way, pursuing a division (which in possibility we have 

 before stated the grounds for believing infinite), we may conceive 

 how each thousandth part of a drop of the water may come to 

 possess a portion of the acid proportionately (according to the 

 aggregate differences) less than itself. This then is the solution 

 of the difficulty: by whatever test we examine this acidulated 

 water, whether directly by the sense of taste, or by a cyhmieal 

 agent, the acid will be discoverable in the minutest portions; not 

 because there are not particles of the water which are unaffected 

 by the acid, but because there is no test adapted to our faculties 

 or comprehension, the minuteness of which is sufficient to dis- 



