678 



Professor J. A. Flenmig 



[May 24, 



are satisfied that this method of signalling is of the greatest utility, 

 and there is no need to remind you of the evidence of this furnished 

 in the recent Russo-Japanese war. No modern liner or large passenger 

 vessel is now complete without a wireless telegraph equipment, and 

 an elaborately organised system of communication has been created 

 by the Marconi Company in connection with this marine telegraphy. 

 Concurrently with this practical development of the art, much 

 scientific investigation has been conducted, having for its object 

 the elucidation and measurement of the various physical operations 

 involved, as well as further improvement. There comes a time in the 

 history of every applied science when the ability to measure precisely 

 the effects concerned is a condition of further progress. It is this 

 alone which enables us to test our theories, or hold in leash hasty 

 opinions as to the possibilities of the invention. 



Fig. 1. 



Lines of Electric Force round an Antenna before Discharge. 



In considering, then, during the present hour some of the recent 

 contributions to this new telegraphy, we may pay a moment's atten- 

 tion to the nature of the things or effects in it which can be measured. 

 An essential element in all electric wave telegraphy is the elevated 

 insulated wire or wires called the antenna, in which high frequency 

 electric currents are set up, and from which the electric waves radiate. 

 Consider a long vertical wire, insulated completely from the earth and 

 charged with electricity (see Fig. 1). There must be somewhere on the 

 surface of the earth nearby a charge of opposite sign. If the wire is 

 negatively charged, then, on its surface, there is, according to modern 

 views, an excess of negative ions or electrons, and on the ground 

 surface round the wire there is a deficiency, that is, there is a positive 

 charge. Furthermore, in the interspace around the rod there is a 

 state of strain of some kind distri])utcd along certain curved Hues, 

 conmionly called lines of electric force. From one point of view 

 these lines may be regarded simply as a convenient mode of 

 delineating the direction of the strain, having not more material 

 reality than lines of latitude and longitude. There are, however, 



