Coupled Vibrations by means of a Double Pendulum. 567 



Another important feature of this thin twin plane is the 

 asymmetric laminary diffraction* pattern to be observed 

 near the two edges of the twin plane, with a beam of light 

 incident normally upon the surface of the crystal. This 

 problem, however, is under investigation. 



The experimental work described in this paper was carried 

 out in the Palit Laboratory of Physics and the writer wishes 

 to express his thanks to Prof. C. V. Raman for kindly 

 providing all facilities for work. 



University College of Science, Calcutta. 

 24th August, 1921. 



LXVI. Coupled Vibrations by means of a Double Pendulum. 

 By A. L. Narayan, M.A.\ 



[Plates X. & XL] 



FOPt the production of high-frequency oscillations re- 

 quired in radio-telegraphy, one of the most important 

 elements in the oscillation circuit is the oscillation-trans- 

 former, which is simply a magnetically-coupled oscillating 

 circuit possessing a primary and a secondary each containing 

 inductance and capacity in series. In order to elucidate and 

 interpret the theory of these electric circuits and illustrate 

 how, when oscillations are excited in one circuit, these "two 

 circuits act and react on each other so that the result is that 

 oscillations of two different periods are set up in both circuits, 

 one greater than and the other less than the natural period 

 of either circuit taken separately, mechanical systems were 

 described bv Prof. Thomas Lyle, Phil. Mag. vol. xxv. pp. 567— 

 572 (Aprif 1913) : Prof. Barton and Miss Browning, Phil. 

 Mag\ vol. xxxiv. p. 24,6 (1917), vol. xxxv. p. 62 (1918), 

 and vol. xxxvi. p. 36 of the same year ; and Mr. Jackson, 

 Phil. Mag. March and September 1920. 



In this paper the author describes an entirely different 

 kind of mechanical system, which gives results very similar 

 to those obtained by Prof. Barton and Miss Browning, and 

 Mr. Jackson, in the papers referred to above. At the same 

 time, the whole arrangement is more neat and much simpler 

 than the very elaborate one adopted by Mr. Jackson, and the 

 method of photographing the vibrations in the present case 

 is essentially different from that of the previous authors. 



The coupled system treated in these pages consists, as shown 

 in the tw T o diagrams (PL X.), of two rigid pendulums A and B r 



* P. N. Ghosh, Proc. Roy. Soc. A, vol. xcvi. (1919). 

 t Communicated by the Author. 



