PROCEEDINGS OF SECTION A. 



33 



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 



(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 that if T be the kinetic, and V the potential 

 energy of either system, then 



2T = K^E^ I ^^^ sin2 w^t + ^-Zl^ sin2 w^t I 

 I c c ) 



2V = K^E^ \ *~-^cos2wii + 

 l c 



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 therefore be useful in demonstrating 

 many of the properties and much of the behaviour of such coupled 

 circuits. 



Its construction is so simple that any one 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 is made from two Starritt's 4-ft. straight edges by fixing 

 them rigidly by means of aluminium distance pieces and clamps so that 

 they are parallel to each other, 3|- inches apart, and so that their 

 "edges " are in a plane which "is perpendicular to the face of either 

 straight edge. The " edges " of the beam near each of its ends rest 

 and roll on the spindle (overhanging) joining two equal steel disc 

 wheels while the latter rest and roll on a bed of good plate-glass firmly 

 supported and carefully levelled. Great care was taken in the con- 

 struction of the rollers. The wheels in each roller were made from 

 5-in. slotting cutters (|- inch thick) after grinding off the teeth, and were 

 fixed If inches apart. The steel spindle was slightly over ^ inch in 

 diameter and overhung the wheels on either side by H inches. The 

 wheels and spindle were ground and the whole roller was trued up so 

 that the diameters of the wheels were equal, the axle uniform in 

 diameter, and all parts circular and coaxal. 



The bed on which the wheels run consisted of a sheet of good 

 plate-glass 4 ft. 6 in. by 6 inches, set in a rigid frame, so as to prevent 

 any tendency towards flexure, and was supported about 3 feet above a 

 table, and carefully levelled. 



To the upper side of the beam are attached two cross rods of wood, 

 one near each end, and both perpendicular to the axis of the beam. 

 6117. B 



