On Machines in General* koi 



consist, will remain unsupported ; for if the above-men- 

 tioned fits have no existence, the whole foundation on which 

 the theory of the size of such parts is placed, will be taken 

 away, and we shall consequently have to look out for a 

 more firm basis on which a similar edifice may be placed. 

 That there is such a one we cannot doubt, and what 1 have 

 already said will lead us to look for it in the modifying 

 power which the two surfaces, that have been proved to be 

 essential to the formation of rings, exert upon the rays of 

 light. The second part of this paper, therefore, will enter 

 into an examination of the various modifications that light 

 receives in its approach to, entrance into, or passage by, 

 differently disposed surfaces or bodies ; in order to discover, 

 if possible, which of them may be the immediate cause of 

 the coloured rings that are formed between glasses. 



XLIII. Essay upon Machines in General, Bij M. Carnot, 

 Member of the French Institute, ^c. ^c, 



[Continued from p. 158.] 



X. J. HE science of machines in general is therefore re- 

 duced to the following question r 



** Being acquainted with the virtual movement of any 

 system of bodies {that is to say,, that movement which each 

 of these bodies tvaidd take if it ivere free), find the real move^ 

 ment which will take place the instant following, on account 

 of the reciprocal action of bodies^ by considering them suck 

 as they exist in nature y i.e. as endowed with all the inertness 

 common to all the particles of matter,** ;/ Wij) I 



XI. Now, as this question evidently contains, the whole 

 of mechanics, we must, in order to proceed with precision,. 

 go back to the first laws which nature, observes in the com- 

 munication of movements. We may reduce them in general 

 to two, which are the following : 



FUNDAMENTAL LAWS OF EQUILIBRIUM, AND MOTION. 



First Law.— ^c^iow and Reaction are always equal and 

 contrary. 



This 



