1007.] on Recent Contrihutions to Electric Wave TeJegraphy. 



■05 



opposite in direction to that in the side of the square (say, the 

 right-hand side) to which it is in proximity. Then the magnetic 

 field of this straight current is from the spectator at the right- 

 hand side, and to the spectator on the left-hand side. Accordingly, 

 the total field on the right-hand side, due to the currents in the 

 closed and open circuits together, is less than that on the left, be- 

 cause the individual fields are added on one side and subtracted on 

 the other. Since the two oppositely directed currents in the adjacent 

 wires may be imagined to come so close as to annul each other, 

 and since the parts of the remainder below ground may be con- 

 sidered to be removed without affecting the field above ground, we 

 arrive at the conclusion that an antenna partly vertical and partly 



,350° l(f 



200"l90°180n70^'«<^ 



Fig. 18. 

 Radiation in various Azimuths from Marconi Bent Antenna. 



horizontal radiates most strongly in the direction opposite to that in 

 which the free end points. 



Mr. Marconi discovered this fact experimentally, and made 

 measurements of the currents induced in receiving antenna? placed at 

 equal distances round this bent transmitter, and plotted the results in 

 the form of a polar curve (see Fig. is). As a quantitative recei\'ing 

 detector he made use of a Duddell's thermal ammeter. In repeating 

 and confirming these experiments on a smaller scale last summer in 

 the grass quadrangle of University College, I employed a form of 

 thermal ammeter of my own design, made as follows : A vacuum 

 vessel made like those which Sir James Dewar devised for storing 

 liquid gases has four platinum wires sealed through the bottom of the 

 inner test tube. One pair of these is connected in the vacuous space 

 by an extremely fine constantin wire and the other pair by a fine 

 tellurium-bismuth thermo- junction, with the junction resting on the 

 Vol. XVIII. (No. 101) 2 z 



