s«ct. ii.] DISSERTATION SECOND. 45 



stead of conceiving that there resides in body a natural and 

 universal tendency to persevere in the same slate, whether 

 of rest, or of motion, they believed that terrestrial bodies 

 tended naturally either to fall to the ground, or to ascend 

 from it, till they attain their own place ; but that, it they 

 were impelled by an oblique force, then their motion be- 

 came unnatural or violent, and tended continually to decay. 

 With the heavenly bodies, again, the natural motion was 

 circular and uniform, eternal in its course, but perpetually 

 varying in its direction. Thus, by the distinction between 

 natural and violent motion among the bodies of the earth, 

 and the distinction between what we may call the laws of 

 motion in terrestrial and celestial bodies, the ancients threw 

 into all their reasonings upon this fundamental subject a 

 confusion and perplexity, from which their philosophy never 

 Was -delivered. 



There was, however, one part of physical knowledge in 

 which their endeavours were attended with much better 

 success, and in which they made important discoveries. 

 This was in the branch of Mechanicks, which treats of the 

 action of forces in equilibrio, and producing not motion but 

 rest ; — a subject which may be understood, though the laws 

 of motion are unknown. 



The first writer on this subject is Archimedes. He 

 treated of the lever, and of the centre of gravity, and has 

 shown thai there will be an equilibrium between two heavy 

 bodies connected by an inflexible rod or lever, when the 

 point in which the lever is supported is so placed between 

 the bodies, that their distances from it are inversely as their, 

 weights. Great ingenuity is displayed in this demonstra- 

 tion ; and it is remarkable, that the author borrows no 

 principle from experiment, but establishes his conclusion 

 entirely by reasoning a priori. He assumes, indeed, that 

 equal bodies, at the ends of the equal arms of a lever, will 



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