166 Br, J. A. Fleming [:May 30, 



Theories of Electricity. 



Various answers Lave been given at different times to the question 

 — What is electricity ? It has been defined as an imponderable fluid, 

 as a force, as a mode of motion, a form of energy, an ether strain or 

 displacement or a molecular motion. 



At one time physicists have considered it as a single entity or 

 fluid ; at others it has been pronounced to be duplex in nature, and 

 positive and negative fluids or electricities have been hypothecated. 



The state of electrification has been looked upon at one period as 

 due to an excess or defect of a single electricity, at others as a conse- 

 quence of the resolution of some neutral fluid into two components. 

 An electrical charge on a conductor has been regarded as something 

 given to or put upon the conductor, and also as a state of strain or 

 displacement in the surrounding non-conductor. The intelligent but 

 non-scientific inquirer is often disappointed when he finds no simple, 

 and as he thinks essential, answer forthcoming to the above question, 

 and he asks why it cannot be furnished. 



We must bear in mind, however, that scientific hypotheses as to 

 the underlying causes of phenomena are subject to the law of evolution 

 and have their birth, maturity and decay. Theory necessarily suc- 

 ceeds theory, and whilst no one hypothesis justified by observations 

 can be looked upon as expressing the whole truth, neither is any likely 

 to be destitute of all degree of truth if it sufficiently reconciles a large 

 number of observed facts. 



The notion that we can reach an absolutely exact and ultimate ex- 

 planation of any group of physical effects is a fallacious idea. We 

 must ever be content with the best attainable sufficient hypothesis that 

 can at any time be framed to include the whole of the observations 

 under our notice. Hence the question — What is electricity ? — no more 

 admits of a complete and final answer to-day than does the question 

 What is Life ? Though this idea may seem discouraging, it does 

 not follow that the trend of scientific thought is not in the right 

 direction. We are not simply wandering round and round, chasing 

 some elusive will-o'-the-wisp, in our pursuit after a comprehension 

 of the structure of the universe. Each physical hypothesis serves, 

 as it were, as a lamp to conduct us a certain stage on the journey. 

 It illuminates a limited portion of the path, throwing a light before 

 and behind for some distance, but it has to be discarded and 

 exchanged at intervals because it lias become exhausted and its work 

 is done. 



The construction and testing of scientific theories is therefore an 

 important part of scientific work. The mere collection of facts or 

 even their utilisation is not the ultimate and highest goal of scientific 

 investigation. The aim of the most 2ihilosoi)hic workers has always 

 been to penetrate beneath the surface of phenomena and discover 

 those great underlying fundamental j^rinciples on which the fabric 

 of nature rests. From time to time a fresh endeavour has to be made 



