OF NATURAL PHILOSOPHY. 131 



to accompany lightning, is a remnant of the theory 

 which made thunder and lightning the explosion of 

 a kind of aerial gunpowder, composed of sulphureous 

 and nitrous exhalations. There are some subjects 

 particularly infested with this mixture of theory in 

 the statement of observed fact The older che- 

 mistry was so overborne by this mischief, as quite 

 to confound and nullify the descriptions of innumer- 

 able curious and laborious experiments. And in 

 geology, till a very recent period, it was often ex- 

 tremely difficult, from this circumstance, to know 

 what were the facts observed. Thus, Faujas de St. 

 Fond, in his work on the volcanoes of central 

 France, describes with every appearance of minute 

 precision craters existing no where but in his own 

 imagination. There is no greater fault (direct falsi- 

 fication of fact excepted) which can be committed 

 by an observer. 



(126.) When particular branches of science have 

 acquired that degree of consistency and generality, 

 which admits of an abstract statement of laws, and 

 legitimate deductive reasoning, the principle of the 

 division of labour tends to separate the province of 

 the observer from that of the theorist. There is no 

 accounting for the difference of minds or inclin- 

 ations, which leads one man to observe with inter- 

 est the developements of phenomena, another to 

 speculate on their causes ; but were it not for this 

 happy disagreement, it may be doubted whether the 

 higher sciences could ever have attained even their 

 present degree of perfection. As laws acquire ge- 

 nerality, the influence of individual observations be- 

 comes less, and a higher and higher degree of 

 K 2 



