CONDENSER OF FORCE'S. ^75 



dually increafed, and that in proportion to the force which 

 the vapour exerts. Therefore vapour of the lead poffible force 

 can, in fuch circuraftances, extend the pores of air. Q, E. D. 

 I remain your's, 



J. DALTON. 

 Manchefter, Nov. 15, 1804-. 



XIV. 



Sotm Account (^a Condenfer of Forces, or a Method of ohtaiti* 

 ing the greateji pojible Efftii from a firfi Mover, of which the 

 Energy is fuhjed to Increafe or Diminution within certain 

 Limits; and in general to vary at Pleafare the Rejijiance to 

 which the Effort of the firft Mover forms an Equilibrium in 

 <Lny Machine whatever, without changing any Fart of the Con^ 

 Jirudiion. Pj^ R. Prony.* 



JL HE problem of mechanics, of which the folution is here Problems la 

 jgiven, is one of the fmall number of thofe which, leading to"^^^^*"**'* 

 refults independent of the particular mechanifm of the ma- 

 chine to which they are applied, prefent, in their folution, a 

 generality which may be compared with that of the rational 

 mechanics, or analyfis. 



It may be enunciated in the following terms : 



*' Any machine being conftru6ted, to find, without making enunciated, 

 any change in the confl:ru6lion, a means of tranfmitting to it 

 the adion of the firft mover, by fulfilling the following con- 

 ditions ; viz. 



'* I. That it may be poffible at pleafure, and with greatCondltions* 

 fpeed and facility, to vary the refiftance (againft which the 

 effort of the firft mover muft continually make an equilibrium) 

 in limits of any required extent, 



" 2. That the refiftance being once regulated, (hall be ri- 

 goroufly conftant until the moment when it is thought proper 

 to increafe or diminith the fame. 



'• 3. That in the moft fudden variations of which the effort 

 of the firft mover may be capable, the variation in velocity of 

 the machine ftiall never undergo a folution of continuity." 



♦ From the Bulletin of the Philomatiuc Society at Paris, 

 No. 83, 



T 2 I ftiaU 



