494 



SCIENCE 



[N. S. Vol. LIII. No. 1378 



in organ pipes lias been very fruitful ; but 

 these results will have to be omitted here. 



9. Beversal of Poles of Telephone Changes 

 Sign of Fringe Deflection. — An earlier de- 

 tection of this result would have saved me 

 mucb mystification. Not expecting it, I did 

 not look for it; but it seems that a reversal 

 of the telephone current (so to speak) reverses 

 the fringe deflection, symmetrically. It is 

 merely necessary to add a switch to the tele- 

 phone circuit to prove this. Moreover for a 

 given position of the switch and in the 

 proper order of frequency, pressure incre- 

 ments pass continuously into pressure decre- 

 ments (Fig. Y). 



To test the case further, I used the motor 

 interrupter, making a survey for frequencies 

 between g' and a" with the switch reversed 

 and the sealed telephone. The new curve 

 corresponded very fully to the curve. Fig. 7, 

 except that maxima and minima had been ex- 

 changed. Thus the apparatus regarded as a 

 dynamometer would, with a proper selection 

 of frequency, give both quantity and sign of 

 the impulsive currents in the telephone. 



Since the resonating region B is vented by 

 the pinhole, the positions of equilibrium of 

 the quiet and of the vibrating plate are in- 

 effective. Hence it is necessary to assume 

 that the vibrations of the plate are here not 

 symmetrical; or that, for instance, the im- 

 pulse corresponding to the break of current 

 at the interruptor is of excessive importance. 



A closed region may be filled with an ex- 

 cess of compressed wavefront successions, pro- 

 vided means are at hand for the supply of 

 the extra air needed and the energy dissi- 

 pated; conversely, the closed r^on may be 

 filled with an excess of rarified wavefront suc- 

 cessions if the outflow of superfluous air is 

 possible. In both cases the vent must be so 

 small as to leave the region virtually closed. 

 A ray of light imprisoned in a chamber closed 

 with perfect mirrors might be considered as 

 analogously circumstanced. 



10. Bemoval of Pressure Decrements Asso- 

 ciated with Pressure Increments. — Marked 

 pressure decrements occur near the minima 

 at c" and a" in case of the prolonged tests 



in §8. One may, therefore, susi)ect that (as 

 in §Y), the decrements result from an insuffi- 

 ciently tight joint at the telephone plate. The 

 telephone with sealed plate was, therefore, 

 carried through the chromatic series of notes 

 from /' to a". It is needless to give the data 

 here, because they resembled Figs. 7 and 8 

 in character, except (as was anticipated) that 

 there were no pressure decrements at the 

 minima. In fact the maxima (below /' at c", 

 g" and above a") came out more sharply than 

 in Figs. Y, 8 and the now positive minima 

 (near g' , d" , a") equally so. It seems as if 

 the ordinary overtones in the key of C were 

 in question. 



Eeplacing the sealed telephone by the usual 

 apparatus with clamped plate, the results of 

 Figs. 7, 8 with marked dilatations at the 

 minima were reproduced at once, except that 

 the maxima {a', c" , a") were in the key of A, 

 in accordance with the increased volume. 



Finally I tested the above telephone with 

 sealed plate again and found that pressure 

 decrements at the minima associated with 

 pressure increments at the maxima (as in 

 Figs. 7, 8) had reappeared. These relations 

 were exchanged on reversing the current. I 

 suspect, therefore, that the potent influence is 

 the mode of vibration (modified by sealing) of 

 the telephone plate itself. About this I shall 

 have something to say in the near future, 

 showing that each inductive impulse is fol- 

 lowed by shock waves in the plate, of rela- 

 tively very high frequency compared with the 

 frequency of induction, just as an anvil rings 

 after each blow of the hammer. 



Carl Barus 



Brown Univeesitt, 

 Peovidence, E. I. 



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