46 The Realm of Nature CHAP. 



obtain a small fraction of its equivalent of work. As water 

 tends to flow to the lowest level, so in Nature energy of 

 every kind tends to assume the least available form, which 

 is that of heat. This process is called the degradation of 

 energy, and in course of time, if it continues to act, all the 

 energy of the Universe will be reduced to the form of heat- 

 vibrations in one uniform mass of matter at one uniform 

 temperature, and although present in full amount quite 

 unavailable for doing work. Viewing the past of the 

 Universe in the light of the degradation of energy, Sir 

 William Thomson has shown that there was a time when 

 the distribution of heat was such as could not have been 

 derived from any conceivable previous distribution ; in other 

 words, that there was a beginning or a creation and that ever 

 since the Universe has been like a machine running down. 



76. Electrical Energy is not yet sufficiently understood 

 to admit of its nature being simply explained. It seems 

 to be the energy of any form of stress or motion of the 

 ether. Electricity is often spoken of as a fluid, but this 

 is simply the survival of a more dense ignorance of its 

 nature. Electrical energy appears to take part in nearly 

 every change of matter as to composition or state. It has 

 the power of decomposing many chemical compounds which 

 resist the action of every other form of energy, and it can 

 also make some elements combine together which do not 

 unite by any other means. As heat is transmitted from 

 matter at a high temperature to matter at a low tempera- 

 ture, so electricity passes from matter at a high electrical 

 potential to matter at a lower potential. This passage of 

 electricity is called an electric current. 



77- Conductors and non - Conductors. Electricity 

 passes readily through some substances, such as copper, 

 silver, metals of every kind, sea- water, damp earth, etc., 

 and these are called conductors. Other substances, such 

 as dry air, glass, sealing-wax, allow it to pass with such 

 difficulty that they are called non-conductors. There is no 

 perfect conductor, nor any absolute non-conductor. Even 

 copper and silver offer a certain resistance to the passage 

 of electricity, and if the difference of potential is sufficiently 



