576 Prof. T. R. Lyle on Mechanical Analogy to the 



As a test of the accuracy of these conclusions it is easy to 

 show that T, the kinetic energy of the pendulum system 

 given in § 3, can be easily reduced, by aid of the relation at 

 the end of § 5, to the form 



iLxC^ + MCA + iLaC 



(the expression for the kinetic energy of the circuits) , where 

 the symbols in this expression represent their analogous 

 quantities given above. It is also easy to show T that if T be 

 the kinetic and V the potential energy of either system > 

 then 



2T = K : E 2 { ~ sin 2 co } t + — sin 2 co 2 t j 



2 V = K X E 2 1 — cos 2 <o t t + — cos 2 co 2 t | . 



7. It should now be admitted that the mechanical system 

 or model proposed is a perfect analogue to the coupled 

 circuits of a Marconi transmitter. The model should there- 

 fore be useful in demonstrating many of the properties and 

 much of the behaviour of such coupled circuits. 



Its construction is so simple that anyone can design a 

 suitable apparatus for himself if he takes sufficient care to 

 minimize friction. A description of the model that I have 

 found satisfactory may, however, be desirable. 



The beam consists of a square brass tube 1 in.x 1 in. x 

 18 in., to the two opposite sides of which are screwed and 

 sweated four short steel straight edges to act as runners, two 

 near each end with their running edges projecting below the 

 lower face of the beam. The bearing edges of these runners 

 are all carefully scraped so as to be straight and to all lie in 

 a plane parallel to the upper surface, and to the axis of the 

 beam. The pair of runners at each end now rest on the 

 cylindrical steel spindle -f^ in. in diameter joining two light 

 but rigid brass disk wheels each 2\ in. in diameter. Great 

 care was taken to have the surfaces of the spindles and the 

 rims of the wheels coaxial, and to have the diameters of the 

 wheels and spindles that support one end of the beam exactly 

 equal to those of the wheels and spindle that support the 

 other end. 



The wheels run on a bed made of a strip of good plate 

 glass 30 in.x 3 in. firmly supported so as to prevent any 

 tendency towards flexure, about 3 feet above a table, and 

 carefully levelled. 



To the upper side of the beam are attached two cross 



