708 Professor J. A. Fleming [May 24, 



easily located. It will be seen, therefore, that two well defined 

 principles had been arrived at by Marconi. First, that the non- 

 symmetry of the radiation and reception depends upon the employ- 

 ment of antennae having their horizontal portions large compared 

 with the vertical, and secondly, that the maximum radiation is in the 

 direction opposite to that in which the free end of the horizontal 

 part points. These observed effects rest on a sound scientific basis, 

 and, as I have shown, are immediately derivable from first principles. 



Previously to Marconi's experiments no definite guiding principles 

 as to directive telegraphy had been published, but a number of un- 

 connected observations made, not always correctly interpreted or 

 even described, and in any case with limited application. 



Meanwhile, however. Professor F. Braun, of Strassburg, had been 

 engaged on a different plan for directing the radiation from antennae. 

 Briefly stated, his method is as follows : He erects three vertical 

 antennas at the corners of an equilateral triangle, or four at the 

 corners of a square, the sides of which are about equal to the height 

 of the antennae, and he creates in them electrical oscillations which 

 have a defined and constant difference of phase by methods contrived 

 by him, Drs. Papalini and Mandelstam, not yet fully described. It 

 is found that the waves sent off from these three antennie interfere 

 with each other in an optical sense, exalting each other in some 

 directions and nullifying each other in other directions, in accordance 

 with their relative amplitude and phase difference. The resultant 

 effect can be so arranged that the radiation is extremely un- 

 symmetrical, being much more towards one side than the other. The 

 intensity in various azimuths may be represented by the radii vectores 

 of a sort of oval or heart-shaped curve, the triple transmitter 

 occupying a position on the cusp or apex of the curve (see Fig. 22). 

 It will be seen, tlierefore, that popular notions on the subject of 

 directive telegraphy are wide of the mark. Whilst we cannot yet 

 project a narrow beam of long-wave electric radiation in any required 

 direction, or focus it entirely on a given receiving station at a great 

 distance, much can be done to prevent radiation being sent out from 

 transmitters in directions in wliich it is of no use or not desired. 



At Coast Stations communicating with ships at sea something has 

 ah'eady Iteen done to achieve this result. Mr. Marconi has for some 

 time past employed such directive antennas at liis large power stations 

 ;>t Poldhu and (elsewhere. 



These, then, are a few of the contri])utio?is whic^li Inivc recently 

 been made by practicians and tlieorists to this fascinating and pro- 

 gressive subject. But, whilst we may congratulate ourselves that 

 progress continues to be made, there are still large districts of it in 

 which our knowledge is most inc()mi)lete. One matter having a very 

 pi-actical bearing is the necessity for systematic study of the causes 

 which vary the transparency of space to long electric waves. You 

 will continually see references in the daily papers to isolated feats of 



