INTRODUCTION xiii 



that they are immutable. On this single base rests 

 the whole of Science. The answer that is wrung 

 from Nature by an experiment to-day holds good 

 for all time. The numberless errors into which 

 scientific men have fallen and into which for a 

 time they may have led the scientific beliefs of 

 their generation are due to their misunderstanding 

 the answer which Nature has given, and these 

 errors are inevitably dorrected by others who have 

 put the question more skilfully or have more 

 accurately read the answer. The replies that she 

 gives to our questions are always truthful and will 

 therefore in due time be recognised as consistent. 



These laws of Nature are but another name for 

 that which I have already referred to as the wealth 

 of the world in which we live. The properties of 

 every element and of every combination of elements 

 are just as much included in this totality of the 

 laws of Nature as is the law of gravitation. This 

 our prison-house is .furnished with collections and 

 combinations of substances governed by immutable 

 laws which they obey under whatever circumstances 

 we call upon them to do so. The knowledge of 

 these immutable laws these properties of sub- 

 stances is the whole of our wealth and it is the 

 conscious or unconscious utilisation of them which 

 constitutes all the achievements of mankind. 



The main charm of this collection of Essays is 

 the presentation of the manner in which this inves- 

 tigation of the furniture of the world has already 



