46 Prof. Barton and Miss Browning on Coupled 



at this instant lost all amplitude, and it was then suddenly 

 raised by hand and held in this position while the other bob 

 oscillated with the single period. Fig. 6 (PL II.) is a 

 photographic reproduction of the sand traces thus obtained. 

 The lower trace represents the quenched spark and the upper 

 one shows the vibrations set up in the secondary circuit or 

 antenna. 



IV. Portable Apparatus. 



The work with the double-cord pendulum up to fig. 12 

 inclusive was done with a rough apparatus suspended from 

 beams of the roof. At this point it seemed desirable to 

 have an apparatus that was portable and so arranged as 

 to facilitate the various adjustments required. This was 

 accomplished by the new apparatus shown in fig. 13 (PL V.). 



It consists essentially of a braced framework of deal, 

 one and a half inches square, the main rods being each 

 six feet long. The bridles are of whipcord and fastened 

 off on cleats fixed on the end frame. The pendulum suspen- 

 sions in actual use are wires of various lengths with hooks at 

 •each end, the fine adjustment being attained by a thin cord 

 and tightener as used for tent ropes. In the photograph 

 these working bridles and suspensions would have been 

 scarcely visible and so were replaced by coarse white cords. 

 The two longitudinal rods at the base of the frame are 

 provided with rails made of hoop-iron set edgewise and let 

 into saw-gates along their length. These rails carry four 

 ball-bearing sheaves, which are fixed on the under side of 

 the board 31 by 23 inches arranged to carry the detachable 

 cards which receive the sand traces. To draw this board 

 along, a cord passes from the centre of one end through two 

 tension-eyes to a bobbin on one side of the end frame. This 

 bobbin is turned by a handle slowly or quickly as may be 

 desired for the purpose in view. 



V. Coupling Graph for Cord and Lath Pendulum. 



Both in the electrical case and for the double-cord 

 pendulum the coupling may approach but cannot reach 

 the value unity. But in the case of the cord and lath 

 pendulum the conditions are somewhat different ( see 

 <pp. 258 and 259, Phil. Mag. October 1917). Thus we have 



1 + a + a 2 ' 



