408 ACTUAL WORKING IN ORIGINAL RESEARCH. 



perception and consciousness. Every diminution in the 

 number of attributes of an idea below a certain extent, 

 diminishes mental excitement and perception ; and dyna- 

 mic phenomena may be considered as being less abstruse 

 but more complex, because they possess the additional 

 attribute of motion. And as the usual order of discovery 

 and exposition is from the easy to the difficult, from the 

 evident to the obscure, and statical molecular phenomena 

 are often less manifest to the senses than dynamical ones,- 

 dynamical causes may be conveniently considered before 

 the more recondite statical conditions. 



The number of possible causes of physical or chemical 

 phenomena and the number of possible effects of causes 

 are fixed ones, because the Great C'ause of all things acts 

 by means of definite forces according to definite laws ; 

 and the number of these forces and laws, and of their 

 combinations and permutations, which regulate a finite 

 number of substances and actions, although exceedingly 

 large, is probably not unlimited. 1 We know of only one 

 force of gravity, and one chief law of its action ; and the 

 known laws, according to which either of the physical 

 forces may be produced or operate, are but few. For a 

 similar reason also the number of immediate causes of a 

 given effect, or of immediate effects of a given cause, are 

 limited. 



The total number of causes in nature is, however, 

 extremely great, and are as varied as the phenomena they 

 produce ; they are of different kinds, and, in accordance 

 with the foregoing definition, they may be primarily 

 classified according to the various forces of nature, viz. 

 gravity, mechanical force, cohesion, adhesion, light, heat, 

 electricity, magnetism, chemical affinity, vital and mental 

 power. They may also, for the purpose of exposition, be 



1 See Chapter II. pp. 15, 16. 



