46 HISTORY OF MECHANICS. 



thrown or pushed must react 13 against that which 

 pushes it ; and that a body so large as not to yield 

 at all, or so small as to yield entirely, and not to 

 react, produces no throw or push?" The same 

 confusion of ideas prevailed after his time : and 

 mechanical questions were in vain discussed by 

 means of general and abstract terms, employed 

 with no distinct and steady meaning ; such as im- 

 petus, power, momentum, virtue, energy, and the 

 like. From some of these speculations we may 

 judge how thorough the confusion in men's heads 

 had become. Cardan perplexes himself with the 

 difficulty, already mentioned, of the comparison of 

 the forces of bodies at rest and in motion. If the 

 Force of a body depends on its velocity, as it ap- 

 pears to do, how is it that a body at rest has any 

 Force at all, and how can it resist the slightest 

 effort, or exert any pressure ? He flatters himself 

 that he solves this question, by asserting that bodies 

 at rest have an occult motion. " Corpus movetur 

 occulto motu quiescendo." Another puzzle, with 

 which he appears to distress himself rather more 

 wantonly, is this: "If one man can draw half of 

 a certain weight, and another man also one half; 

 when the two act together, these proportions should 

 be compounded ; so that they ought to be able to 

 draw one half of one half, or one quarter only." 

 The talent which ingenious men had for getting 

 into such perplexities, was certainly at one time 



