Oscillations in Coupled Circuits. 41 



solid carbons (as in the Duddell musical-arc arrangement). 

 and if the smaller leyden-jar is connected to the terminals or! 

 the secondary coil, either o£ two notes, differing in quality 

 and separated in pitch by about a major sixth, may be heard. 

 The pitch o£ the notes is not constant, but fluctuates to some 

 extent, and can be varied by altering the length o£ the arc 

 or the resistance in the supply circuit. 



With these two condensers, which are the same as in 

 Case IV. above, the two notes are equally stable, and the 

 sound may change several times from one note to the other 

 without any " feeding " of the arc, the change being always 

 a sudden rise or fall of about a sixth. 



If the primary capacity is increased to about 14'5 micro- 

 farads, tw T o notes may again be heard but the higher note is 

 less stable than before, and only comes out with a very short 

 arc, and then with difficulty. 



With the primary capacity 9*55 mfd. and the same 

 secondary capacity (as in Case II. above) the lower note is 

 rather less stable than the higher, while with ^ = 9*55 and 

 C 2 = '001063 (Case I.) the lower note is rarely heard. 



It appears therefore that with the coils used in these 

 experiments, when lj i C 1 is nearly equal to L 2 C 2 the two notes 

 are equally stable ; if the ratio of the primary to the 

 secondary capacity is increased, the higher note becomes less 

 stable ; if this ratio is diminished, the lower note sounds 

 less easily. If I^Ci is made either much smaller or much 

 greater than L 2 C 2 , only one note is heard. 



Other pairs of condensers were tried, with similar results. 

 In all cases in which the two notes were heard the interval 

 between them was about a fifth or a sixtli *. 



In PL I., fig. 9, are shown specimens of the photo- 

 graphs obtained when the electrometer was connected to the 

 secondary condenser. The upper curve represents the lower 

 note and the lower curve the higher note, the capacities being 

 C 2 ^= -000875 and 1 about 13*8 microfarads. In fig. 10 

 is shown the lower note curve for the case Ci=ll'87, 

 C 2 = -000875 mfd. 



It will be seen that while the higher note corresponds to 

 an approximately simple oscillation, the curve for the lower 

 note in fig. 9 consists of a succession of well-separated pairs 

 of waves with sometimes two small waves appearing between 

 the pairs. In fig. 10 the pairs of waves are not so well 

 separated, and there are no small waves between them. 



* The arc was supplied by the 200-volt continuous current mains 

 through sufficient resistance. The current in the supply circuit was 

 3 or 4 amperes. The current in the primary circuit was generally 

 greater with the low note than with the high note. 



