442 POPULAR SCIENCE MONTHLY. 



ground, there is a propagation through the earth of electric action, 

 which may consist in a motion or atomic exchange of electrons. Each 

 change or movement of a semiloop of electric strain above ground has 

 its equivalent below ground in inter-atomic exchanges or movements of 

 the electrons, on which the ends of these semi-loops of electric strain 

 terminate. The earth must play therefore a very important part in 

 so-called 'wireless telegraphy,' and we might almost say the earth 

 does as much as the ether in its production. 



The function of the receiving aerial is to bring about a union be- 

 tween these two operations above and below ground. WHien the electric 

 waves fall upon it, they give rise to electromotive force in the receiv- 

 ing aerial, and therefore produce oscillations in it which, in fact, are 

 electric currents flowing into and out of the receiving aerial. We may 

 say that the transmitting aerial, the receiving aerial and the earth 

 form one gigantic Hertz oscillator. In one part of this system, electric 

 oscillations of a certain period are set up by the discharge of a con- 

 denser and are propagated to the other part. In the earth, there is a 

 propagation of electric oscillations ; in the space above and between the 

 aerials, there is a propagation of electric waves. The receiving aerial 

 feels therefore what is happening at the distant aerial and can be made 

 to record it.* 



We have next to consider the question of the wave detecting devices 

 which enable us to appreciate and record the impact of a wave or wave 

 train against the aerial. At the very outset it will be necessary to coin 

 a new word to apply generally to these appliances. Most readers are 

 probably familiar with the term 'coherer,' which was applied by Sir 

 Oliver Lodge, in the first instance, to an electric wave-detecting device 

 of one particular kind, viz., that in which a metal point was lightly 

 pressed against another metal surface and caused to stick to it when an 

 electric wave fell upon it. As our knowledge increased, it was found 

 that there were many cases in which the effect of the electric radiation 

 was to cause a severance and not a coherence, and hence such clumsy 

 phrases as 'anticoherer' and 'self-decohering coherer' have come into 

 use. Moreover, we have now many kinds of electric wave detectors 

 based on quite different physical principles. At the risk of incurring 

 reprobation for adding to scientific nomenclature, the author ventures 

 to think that the time has arrived when a simple and inclusive term 

 will be found useful to describe all the devices, whatever their nature, 

 which are employed for detecting the presence of an electric wave. For 

 this purpose the term Tcumascope, from the Greek y-o:ia (a wave), 

 is suggested. The scientific study of waves has already been called 



* The * earth ' itself probably only conducts electrolyticallv. All such 

 materials as sand, clay, chalk, etc., and most surface soils are fairly good 

 insulators when very dry, but conduct in virtue of moisture present in them. 



