100 PHYSICAL SCIENCES IN ANCIENT GREECE. 



may have pressure without motion, or dead pull, in 

 other cases, as at the critical instant when two 

 nicely-matched wrestlers are balanced by the exer- 

 tion of the utmost strength of each. 



Pressure in any direction may thus exist with- 

 out any motion whatever. But the causes which 

 produce such pressure are capable of producing 

 motion, and are generally seen producing motion, 

 as in the above instance of the wrestlers, or in a 

 pair of scales employed in weighing ; and thus men 

 come to consider pressure as the exception, and 

 motion as the rule; or perhaps they image to them- 

 selves the motion which might or mould take place; 

 for instance, the motion which the arms of a lever 

 would have if they did move. They turn away 

 from the case really before them, which is that of 

 bodies at rest, and balancing each other, and pass 

 to another case, which is arbitrarily assumed to re- 

 present the first. Now this arbitrary and capricious 

 evasion of the question we consider as opposed to 

 the introduction of the distinct and proper Idea of 

 Pressure, by means of which the true principles of 

 this subject can be apprehended. 



We have already seen that Aristotle was in the 

 number of those who thus evaded the difficulties 

 of the problem of the lever, and consequently lost 

 the reward of success. He failed, as has before 

 been stated, in consequence of his seeking his prin- 

 ciples in notions, either vague and loose, as the 

 distinction of natural and unnatural motions, or 





