﻿598 Prof. J. A. Fleming on the Electric 



in the ratio o£ 40 to 100. Experiment shows this to be 

 approximately the case. 



In a further set of experiments a number of measure- 

 ments were made bv erecting a vertical antenna having; 

 a lateral wire terminated in a capacity plate, attached to 

 some point on its height (see figs. 9 to 13, PI. XVII.). In 

 all cases such a transmitting antenna was found to radiate 

 more equally in all azimuths than if the vertical part above 

 the lateral projection was removed. Hence the polar curves 

 are made more nearly circular by adding this vertical part. 

 This showed that strengthening the electric moment of such 

 a bent antenna makes it a less unsymmetrical radiator, and 

 that what is required to improve the simple bent antenna and 

 make it radiate more unequally in a fore and aft direction 

 is an increase in the magnetic moment. 



To investigate this point a little more, the whole of the 

 observations taken with the 20-foot antenna bent over at 

 various heights were plotted to the same scale in a family of 

 polar diagrams together with the results obtained from the same 

 antenna in a vertical position (see Plate XVIII.) . Thus if the 

 20-foot antenna is placed in a vertical position it radiates 

 equally in all azimuths, and the polar curve obtained by plot- 

 ting its field at a constant distance is a circle. If the antenna 

 is bent over, say, 5 feet from the top so that 1 5 feet are vertical 

 and 5 feet horizontal, the radiation is still nearly equal in all 

 directions, but the field is not so great as when the antenna 

 is wholly vertical. Hence the polar curve is smaller than 

 the above circle and not quite circular. If it is bent over at 

 the height of 10 feet, then the polar curve is smaller still, also 

 decidedly non- circular and has little depressions in it. If 

 bent over at 15 feet so that 5 feet are vertical, the polar 

 curve is still less circular. Hence as the antenna is bent 

 over so that less and less of it is vertical and more and more 

 horizontal, the radiation in various azimuths becomes more 

 and more unequal, and has in an increased degree a 

 decidedly minimum value at about 105° reckoning 180° in 

 the direction in which the free top end points. The family 

 of polar curves so obtained and depicted in Plate XVIII. 

 show very well the gradual diminution in the current in the 

 20-foot receiving antenna as the 20-foot bent-over trans- 

 mitting antenna is swivelled round, and they show the g?*adual 

 increase in the asymmetry of radiation in various azimuths, 

 for constant distance between radiator and receiver. 



The curves here given, however, never reach the well 

 defined figure-of-8 form of those given by Mr. Marconi, 

 since he employed a transmitting antenna the vertical part 



