ELECTRONIC THEORY OF ELECTRICITY. 9 



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, 

 however, 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 has 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 utilization is not the ultimate and highest goal of scientific 

 investigation. The aim of the most philosophic workers has always 

 been to penetrate beneath the surface of phenomena and discover 

 those great underlying fundamental principles on which the fabric 

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

 to reconstruct, in the light of newly acquired knowledge, our scientific 

 theory of any group of effects. Thus, the whole of electrical phe- 

 nomena have become illuminated of late years by a theory which has 

 been developed concerning the atomic structure of electricity and this 

 hypothesis is called the Electronic Theory of Electricity. 



The Atomic Theory. 

 The opinion that matter is atomic in structure is one which has 

 grown in strength as chemical and physical knowledge has progressed. 

 From Democritus, who is said to have taught it in Greece, to John Dal- 

 ton who gave it definiteness, and to Lord Kelvin who furnished the 

 earliest numerical estimate of the size of atoms, it has been found to 

 be the best reconciler of very diverse and numerous facts. Let us 

 consider what it really means. Suppose we take some familiar sub- 

 stance, such as common table salt, and divide a mass of it into the 

 smallest grains visible to the eye. Each tiny fragment is as much 

 entitled by all tests to be called table salt, or to give it the chemical 

 name, sodic chloride, as a mountain of the material. Imagine that 

 we continue the subdivision under a good microscope ; we might finally 

 obtain a little mass of about one hundred-thousandth of an inch in 

 diameter, but beyond this point it would hardly be visible even under a 

 powerful lens. We may, however, suppose the subdivision continued 

 a hundred fold by some more delicate means until we finally arrive at 

 a small mass of about one ten-millionth of an inch in diameter. A 

 variety of arguments furnished by Maxwell, Boltzmann, Loschmidt, 

 Lord Kelvin and others show that there is a high degree of probability 

 that any further subdivision would cause the portions into which the 

 salt is divided to be no longer identical in properties, but there would 

 be two kinds of parts' or particles, such that if all of one kind were 

 collected together they would form a metal called sodium, and if all 



