I 



On Machines in General. 20$^: 



id exercised between two bodies which meet, does not de-' 

 pend upon their absolute movements, hut solely upon their^ 

 relative movements. 2. That the force or quantity ofmov^-^^ 

 ment which they exercise upon each other, hy the shock, is' 

 always directed perpendicularly to their common surface at 

 the point of contact. ^>Vi3biP 



XII. Of the two fundamental laws, the first generally 

 agrees with all the bodies of nature, as well as the two se- 

 condary laws which we have seen ; and the second solely 

 regards hard bodies ; but as those which are not hard have 

 different degrees of elasticity, we generally refer the laws of 

 their movement to those of the hard bodies, which we take 

 for a term of comparison, i. e. we regard the elastic bodies 

 as composed of an infinity of hard corpuscles separated by 

 small compressible rods, to which we attribute all the 

 elastic virtue of these bodies ; so that, properly speaking, we 

 do not consider in nature any other than bodies endowed 

 with different moving forces. We shall follow this method 

 as the simplest : we shall therefore reduce the question to 

 the investigation of the laws observed by hard bodies, and 

 shall afterwards make some applications of them to cases 

 in which bodies are endowed with different degrees of 

 elasticity. 



XIII. This essay upon machines not being a treatise 

 upon mechanics, my object is not to explain in detail, nor 

 to prove the fundamental laws I have related ; these are 

 truths which all the world knows, as to which they are 

 generally agreed, and which are most strongly manifested 

 in all the phsenomena of nature. This is sufficient for my 

 object, which is merely to draw from these laws a simple 

 and exact method for finding the state of rest or of move- 

 ment which results from them in any given system of bo- 

 dies, i. e, to present the same laws under a form which 

 may facilitate their application to each particular case. 



XIV. Let us suppose therefore any system of hard bo- 

 dies, the virtual given movement of which is changed by 

 their reciprocal action into another which we wish to find ; 

 and in order to embrace the question in all its extent, l?t us 

 suppose that the movement may either change suddenly, or 

 ; Vol. 30. No. 119.^/?n7 1808. O vary 



