On Machines in General. ■ 223 



the impulse of the wind ; 2d, on the other hand^ the resist- 

 ance of the water increases : consequently these two forces 

 tend to equality : when they have attained this point they 

 will be mutually dcsuoycd; and thcref)re the vessel will be 

 moved as a free body, i. e. its velocity will be constant. 

 If the wind fell, the resistance of the Vvfater would surpass 

 the soliciting force ; the movement of the vessel would 

 slacken ; but, as a necessary consequence of this slackeninsc, 

 the wind would act more efficaciously upon the sails ; and 

 the resistance of the water would at the same time diminish : 

 these two forces would still tend therefore to equality, and 

 the machine would at the same time attain an uniformity of 

 movement. 



L. The same thing happens when the moving forces are 

 men, animals, or other agents of this kind : at first the 

 mover is a little above the resistance j thence arises a sm;dl 

 movement, 'which is gradually accelerated by the repeated 

 efforts of the moving power; but the agent itself is obliged 

 to assume an accelerated movement, in Order to remaia 

 attached to the body upon which it impresses motion. 

 This acceleration, which it procures for itself, consumes a 

 part of its effort, in such a manner that it acts less effica- 

 ciously upon the machine ; and the movement of the latter, 

 accelerating less and less, finishes by soon becoming uniform. 

 For instance : a man who could make a certain effort in the 

 case of equilibrium, would make a much less one if the 

 body he applies his strength to should yield, and if he was 

 obliged to follow it in order to act upon it : it is not because 

 the absolute labour of this man is less ; but it is because his 

 effort is divided into two, one of which is employed in put- 

 ling the man himself in motion, and the other is transmitted 

 to the machine. Now it is from this last alone that the 

 effect is manifested in the object proposed. 



I shall nevertheless continue to consider machines under 

 a more general point of view : thus, I shall place in this 

 scholium several reflections applicable to the varied move- 

 ment. I shall only suppose that this variation takes place 

 by insensible degrees ; and I shall prove that this should in 



V^ol. 31. Nq. I'i3. Aug. 1808. P fact 



