

Applied Science 833 



The aerial consists, in its simplest form, of a length of copper 

 wire suspended by some insulating material from the top of a 

 mast. As the oscillations are transferred from the first to the 

 second coil, they cause a very rapid to and fro movement of 

 electrons to flow along the aerial wire. We have seen that each 

 electron in changing its motion generates a tiny electromagnetic 

 wave. The movements of all the electrons in the antenna produce, 

 therefore, an immense multitude of little waves which combine 

 together to make a big one. 



This wave radiates out from the aerial with the speed of light, 

 that is, at about 186,000 miles per second. The wave is really a 

 wave of electric and magnetic force, and these two forces act in 

 directions at right angles to one another. Both these forces, more- 

 over, are at right angles to the directions of the advancing waves 

 (see Fig. 6 facing p. 828). 



The transmitting apparatus in the operating-room consists 

 essentially of, first, apparatus for charging the Leyden jar, which 

 may be either an induction coil and batteries to work it, or a 

 motor generator which produces an alternating current. This 

 current is transformed to one of a very high voltage or pressure 

 by means of a step-up transformer, as a high voltage current is 

 essential to satisfactorily charge a condenser. A switch or key is 

 provided to make, or break, this charging circuit. Secondly, we 

 have the condenser (for storing electricity), which may be either 

 in the form of a Leyden jar, or jars, or in the form of plate glass, 

 with the tinfoil coatings on either side. Thirdly, there are two 

 coils of wire in close proximity to each other. Sometimes these 

 coils, instead of being made of wire, are made of long metal strips. 

 These coils are the coils used to transfer the oscillations to the 

 aerial circuit. There is also another coil of wire which is used 

 to tune the apparatus. Tuning is explained fully later. Then 

 there is the spark gap, of which there are many different kinds, 

 the simplest being two metal knobs fixed very near to one another. 

 This type is known as the plain discharger. In some makes the 



