SCIENTIFIC PROBLEMS IN RADIOTELEGRAPHY 357 



improvement in the means of detecting these waves but the 

 invention of a radiator which could project them far enough. 



This important step in invention was made by Marconi when 

 he constructed a form of radiator consisting of a long, nearly 

 vertical wire insulated at its upper end and having its lower end 

 connected to one of a pair of spark balls, the other ball being 

 connected to the earth. What was not appreciated before his 

 time was that a vertically arranged Hertzian oscillator of great 

 length, say 100 feet or more, half buried in the earth had the 

 power of producing electromagnetic waves of great energy 

 which could travel over the earth or sea ; also that a similar 

 aerial wire would absorb the radiation and enable it to be 

 detected. When once this clue to success had been provided, 

 the invention of details went on apace and by 1897 or so 

 apparatus for telegraphy without connecting wires over a range 

 of several miles had been fairly well perfected by Marconi, 

 whilst Lodge had also shown how the facts of electrical 

 resonance might be applied to preserve the privacy of communi- 

 cation and the isolation of stations. Leaving out of account 

 details of development and invention, for which special treatises 

 must be consulted, we may say that at the present time (1912) 

 the greater part of all the wireless telegraphy in the world is 

 conducted substantially by means of the following appliances : 

 at every station there is a transmitter and a receiver, each of 

 which consists of three parts. The transmitter comprises : (i) 

 some means of producing a high-tension electric current, 

 whether by alternating current dynamo and transformer or 

 direct current dynamo and storage cells — or in the case of small 

 plants an induction coil and battery ; (ii) a condenser, which 

 may be a collection of Leyden jars or even a large air 

 condenser, which is charged to a high potential by the first- 

 named appliances and then discharged across a spark gap 

 several hundred times a second, (iii) This sudden discharge 

 of the condenser is sent through a coil of wire called an 

 oscillation transformer and is made to create other oscillations 

 of electricity in the third element called the "antenna," which 

 is a long, nearly vertical wire, insulated at the upper end and 

 having its lower end in connexion with the earth or with other 

 wires laid either in or above the earth, called the balancing capa- 

 city. The antenna consists of a number of wires arranged in 

 fan-shape or else rising up and then bent down like the ribs of an 



