LECTURE I. 35 



has , not as yet informed us of more than 

 reason has suggested, from the consider- 

 ation of the general phasnomena of nature ; 

 which is, that the motions and changes oc- 

 curring in surrounding bodies, and in our 

 own, are the results of some subtile sub- 

 stance or substances, which enters into 

 their composition, or acts upon them. 



But if science were eventually to demon- 

 strate that heat, light, and electricity, are 

 different things, that there are various kinds 

 of subtile substances, then I should be 

 obliged to suppose that there was also a 

 subtile substance belonging to living bodies, 

 a principle of life, which had the amazing 

 power of kindling and controlling the de- 

 structive element of fire, and regulating the 

 actions of that still more sudden and power- 

 ful agent, electricity. Neither by so doing 

 should I transgress the rules of philosophy ; 

 for in suggesting a theory, it should not 

 only be probable, but adequate to explain 

 all the phaenomena. 1 am aware, however, 

 that there may be some contemplative and 

 unprejudiced men, who, perhaps a little 



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