Matter and Energy. ' 15 



formed, though only partially, into potential energy. Accord- 

 ing to a law first enunciated by Carnot, it is only when heat 

 passes from a warmer to a colder body, and even then only 

 vpartially, that it can be converted directly or indirectly into 

 mechanical work. That passage, however, cannot be inter- 

 rupted. There is a constant tendency in nature towards 

 the establishment of an equilibrium of temperature ; so that 

 every transformation of energy is accompanied by the dissi- 

 pation of a certain proportion of it into space in the unavail- 

 able form of uniformly diffused heat. It is to be noted that 

 this does not involve a loss of energy ; it merely involves a 

 degradation of energy from an available form into a form 

 unavailable to man. There is never any absolute loss of 

 energy. Like matter, it is indestructible. The relation 

 between the amount of potential and of kinetic energy in the 

 universe is constantly changing the amount of the kinetic 

 energy steadily increasing at the expense of the potential 

 energy. But the sum of the two forms of energy is a 

 constant quantity. This goes by the name of the law of 

 the conservation of energy, and it is one of the most 

 important generalisations to be found in the whole range of 

 science. As stated by Clerk Maxwell, the law may be ex- 

 pressed as follows : ' The total energy of any material system 

 is a quantity which can neither be increased nor diminished 

 by any action between the parts of the system, though it 

 may be transformed into any of the forms of which energy : 

 is susceptible.' 



Although it is true that the sum of the energies of the 

 universe is a constant quantity, yet it must be borne in 

 mind that energy, as has been already stated indirectly, is 

 partly available, partly unavailable, and that energy in its 

 available form is continually becoming less in amount. 



An attempt has been made to measure energy in terms 



ordinary physical or chemical interactions, will form an instructive exer- 

 cise for the junior student, and enable him to become familiar with the 

 transformation of energy in all its aspects. 



