ON THE DISSIPATION OF ENERGY. 453 



might we not annex to it a motor, acting on the 

 same principle as the steam-engine, which would 

 reconvert into motion of the machine the heat 

 which is developed by friction ? Have we not 

 here a good scientific foundation for believing that 

 a fly-wheel set in motion, or clock-work driven by 

 the unwinding of a spring or the running down of 

 a weight, and connected with a heat engine 

 worked by the heat generated by its friction, only 

 wants an impermeable encloser preventing all loss 

 of heat to allow it to go on for ever ? Of course, 

 this impermeable encloser is not realisable, but it 

 is both a scientific and a practical consideration 

 to think what might be done if we had an 

 impermeable substance of which an enclosing case 

 for the instrument could be constructed. We 

 know by the principle of the " Conservation of 

 Energy" that all the energy we gave to the 

 machine is always all there ; some of it in heat 

 and the rest in energy of the weight or spring not 

 quite run down, or in the visible motion of the 

 fly-wheel, or wheels, or vibrating pendulum, or 

 other moving parts of the mechanism. 



