Perpetual Motion 67 



matically any principle that would forbid the invention of a 

 perpetual motion of some hind. Even to-day there are many to 

 whom this appeals, and there are many who look to the direct 

 conversion of heat into electricity, in which every element of 

 heat shall be ttcinsformed into a corresponding element of elec- 

 tricity, so that all the power equivalent to the heat shall be 

 utilized. They do not perceive that this very conversion involves 

 the solution of the problem of perpetual motion. 



Nearly a century ago Sadi Carnot established the fact that 

 the maximum efficiency of a heat engine was that of a reversible 

 cycle, and that any higher efficiency involved the possibility of 

 perpetual motion. He also proved that this efficiency was a 

 function of the range of temperature of the working fluid. The 

 then state of knowledge did not allow him to discover the exact 

 form of the function, but the work of Rankine, Joule, Thompson, 

 and Clausius later showed the form, which is always a fraction 

 having a value less than unity. 



Many inventions have been proposed to contradict or evade 

 Carnot's principle, as, for example, a certain engine of the closed 

 cycle type, exhibited in 1882, in which the inventor was confident 

 of utilizing all the heat contamed in the steam, exce[)t that lost in 

 friction. 



John Bernouilli believed that he had solved the problem by 

 means of an osmotic or filtering membrane. His argument is 

 given in full in his " Opera Omnia" and may be examined in the 

 ^^Encyclopaedia Britannica," but the short explanation following 

 may perhaps be understood. 



Fill an open vessel with a solution of which the solvent is (»f 

 smaller specific gravity than the solution itself. Let an open- 

 ended tube be closed at one end by a membrane which filters the 

 solution, allowing only the solvent to pass through. Both these 

 suppositions are quite possible, and the process is well known and 

 useful in chemical manipulation. If now the tube be plunged, 

 membrane downwards, into the solution, we assume as an axiom 

 that the solvent will pass through the membrane, and will rise in 

 the tube until the column in the tube balances the pressure of the 



