POPULAR SCIENCE MONTHLY. 53 



HERTZIAN" WAVE WIEELESS TELEGRAPHY. VI. 



By Dr. J. A. FLEMING, F.R.S., 



PROPESSOH OF ELECTRICAL ENGINEERING, UNIVERSITY COLLEGE, LONDOK. 



It remains then to consider some of the questions connected with 

 practical Hertzian wave telegraphy and the problem of the limita- 

 tion of communication. These matters at the present moment very 

 much occupy the public attention, and many conflicting opinions are 

 expressed concerning them. 



It may be observed at the outset that the difficulty of dealing with 

 the subject as freely as many desire is that Hertzian wave telegraphy is 

 no longer merely a subject of scientific investigation, but has developed 

 into a business and involves therefore other interests than the simple 

 advancement of scientific knowledge. We can, however, discuss in a 

 general manner some of the scientific problems which present them- 

 selves for solution. The first of these is the independence of com- 

 munication between stations. It is desirable, at the outset, to clear 

 up a little misunderstanding. There is a great difference between pre- 

 venting the reception of communication when it is not desired by the 

 recipient and preventing it when it is the object of the latter to over- 

 hear if he can. It is therefore necessary to distinguish between isola- 

 tion and overhearing. We may say that a station is isolated when it 

 is not affected by Hertzian waves other than those it desires to receive ; 

 but that a station overhears when it can, if it chooses, pick up commu- 

 nications not intended for it, or can not help receiving them against 

 its will. 



This distinction is a perfectly fair one. Any telegraph or tele- 

 phone wire can be tapped, if it is desired, but unless there is some 

 fault on the line, no station will receive a message against its desires. 

 Moreover, it may be noted that there are penalties attaching to tapping 

 a telegraph wire, and at present there are none connected with the mis- 

 appropriation of an ether wave. 



We shall therefore consider in the first place the methods so far 

 proposed for preventing any given receiver from being affected by 

 Hertzian waves sent out from other stations, except that of those from 

 which it is desired to receive them. The first method is that which has 

 been called the method of electrical syntony, and consists in adjusting 

 the electrical capacity and inductance of the various open and closed 



