6 DISSERTATION SECOND. [part i. 



must be the second object of inquiry ; and in this article I 

 shall give an account of Bacon's Philosophy, as applied to 

 Physical investigation. After these two sections, which 

 may in some measure be considered as introductory, I am 

 to treat of Natural Philosophy, under the divisions of 

 Mechanicks, Astronomy, and Opticks. Under the general 

 denomination of Mechanicks I include the Theory of Mo- 

 tion, as applied not only to solids, but to fluids, both incom- 

 pressible and elastick. Opticks I have placed after Astro- 

 nomy, because the discoveries in Mechanicks have much 

 less affected the progress of the former of these sciences 

 than of the latter. To these will succeed a sixth division, 

 containing the laws of the three unknown substances, if, 

 indeed, they may be called substances, — Heat, Electricity 

 and Magnetism. These, though very different, agree in 

 some general characters. They permeate all substances, 

 though not with the same facility ; and, if other bodies had 

 been formed in the same manner with them, the idea of im- 

 penetrability would never have been suggested to the 

 mind. They seem to receive motion, without taking any 

 away from the body which communicates it ; so that they 

 can hardly be considered as inert. Two of them, Heat 

 and Electricity, are perceived by the sense of touch ; but 

 the impression which they make does not convey an idea 

 of resistance. The third is not perceived by touch ; and, 

 therefore, all the three might be denominated impalpable 

 substances. If they have any gravity, it cannot be appre- 

 ciated ; and, for these reasons, had it not too paradoxical an 

 appearance, we might class them together as material, but 

 incorporeal substances. We know, indeed, nothing of 

 them but as powers transferable from one body to another ; 

 and it is in consequence of this last circumstance alone that 

 fhey are entitled to the name of substances. 



Though the general design of this historical sketch ex- 

 tends from the revival of letters to the beginning of (he 



