828 The Outline of Science 



like James Clerk Maxwell and Heinrich Hertz, who were so suc- 

 cessful in investigating the powers and properties of electric cur- 

 rents and magnets. The foundation on which wireless telegraphy 

 is built is electromagnetic waves. In order to understand the 

 principles of wireless telegraphy it is necessary to follow the 

 thought and discovery on which the whole enterprise is based. 

 It is necessary for us, in fact, to become acquainted with one of 

 the greatest and most fundamental branches of modern physics, 

 the science of electromagnetic radiation. The essential charac- 

 teristic of the theory on which wireless telegraphy is based may 

 be put as follows : It directed attention, not so much to electrified 

 bodies themselves, as to the space surrounding them. That is to 

 say, that in the case of an electric current flowing along a wire, 

 for instance, the theory dealt, not with the wire, but with the 

 space surrounding the wire. The wire itself is in a peculiar con- 

 dition, but so is the space about it. This fact, that the space 

 about a wire conveying an electric current has just as remarkable 

 properties as the wire itself, was first completely demonstrated by 

 James Clerk Maxwell, and it is from his epoch-making work 

 that the whole of wireless telegraphy springs. 



Let us consider this theory, not quite in the form in which 

 Maxwell presented it, but from the point of view of the modern 

 electron theory. We know that an electric current may be con- 

 sidered as a flow of electrons, and we know that the electron is 

 the ultimate tiny particle of negative electricity. Now radiating 

 out from any body charged with electricity are lines of force. 

 The magnetic force which exists in circles round an electrified 

 wire is caused by the electric current; the movement or flow of 

 electrons creates a magnetic "field," as it is called, round the 

 path it is supposed that all magnetism is produced in this way. 

 We have seen what lines of force are in the case of a magnet 

 (see figure facing p. 279). The electric lines of force which 

 radiate from any electrified body radiate similarly to those of a 

 magnet. We can picture these lines of force to ourselves as strings 



