CONSERVATION OF ENERGY 225 



First of all it seems perfectly clear that when 

 one form of energy is changed into another, 

 nothing is lost nor is anything gained. Con- 

 sequently the following so-called " laws " have 

 been formulated by men of science : 



1. That the sum of the kinetic and potential 

 energies of any isolated system of bodies remains 

 constant; and 



2. That the sum-total of the energy in the 

 universe remains the same. 



Before considering the bearing of these laws 

 en the question under consideration it will be 

 well to be quite clear in our minds as to what 

 i.5 meant by a law of nature and what its precise 

 value is. 



The word "Law " has two distinct meanings, 

 not unfrequently confounded. Sometimes the 

 term stands for a decree or command, expressed 

 by a sentence in the imperative mood. The Ten 

 Commandments and Acts of Parliament are 

 " laws " in this sense. At other tmes the term 

 denotes some observed uniform mode of action 

 or behaviour in phenomena which is signified 

 by a general proposition in the indicative mood. 

 The laws of chemistry and astronomy are ex- Laws of 

 amples. Now it cannot be too clearly kept in naturc 

 ndnd that the " laws of Nature " are of this 

 latter kind. 



The term simply expresses our appreciation or 



p 



