ACOUSTICS AND GRAVITATION. 63 , 



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when the induction period is but o. i second. The waves observed are imme- 

 diately referable to the natural vibration of the plate of the telephone. They 

 follow a magnetic shock, as the Hertzian waves follow a spark. 



It is now necessary to endeavor to analyze the region x of shattered waves 

 by aid of the screw-iron core described in the preceding paragraph. For this 

 purpose the intemtptor also should run uniformly. If it dips more or less 

 deeply into the mercury, the effect on % is the same as removing or adding 

 resistance to the telephone circuit. By drawing out the fringe band to a limit, 

 one gets a great variety of results ; but their appearance on the average is as 

 shown in figure 90. 



The phenomenon usually begins with an undisturbed fringe a, meaning the 

 objective begins on its path before the inductive shock arrives at the telephone. 

 After this a series of about 6 discontinuous wave-forms (b to c) of rapidly 

 decreasing amplitude appear. Only the inclined and nearly straight parts 

 (6, b', etc.) of the fringe band are visible, so that these waves drop off sheer and 

 are akin to the faulted waves described above (figs. 85 and 86) . The slope of b 

 is accidentally sometimes upward and at other times downward, throughout ; 

 but the slope of b and b' is always symmetrical. 



At cc' these linear groups begin to coalesce and coalescence is about complete 

 at d, though the arch is often seen to open. Beyond d the waves are a suc- 

 cession of smooth flat cycloids with the elevation rapidly dying out toward the 

 center of the field. If the slope of b is downward, then waves are festooned. 



The endeavor to obtain further information by working through a capacity 

 failed. The whole display is seen through 0.05 microfarad about as well as if 

 there were no interruption. With very small capacities, however, the tele- 

 phone still sounds when the fringe bands are quite straight. 



56. Large frequencies. Musical notes. In all the above cases the impulses 

 were distinct and the shock- waves had time to subside in the interval between 

 the impulses. This will no longer be the case when the frequency is much 

 increased. There must then be a coalescence into a single wave phenomenon. 



The attempts to trace this through with the motor contact breaker used 

 above did not succeed. The period of the objective being 7 = 0.34 second, the 

 note g' in the telephone showed uneven waves and suggestion of cross-hatching 

 when the T amplitude was small. At d" there were lines and pulses; but very 

 little was to be inferred as a whole from the compound wave-trains obtained. 



This interrupter was therefore replaced by a small magneto inductor, which, 

 as a rule, gave compound but otherwise unbroken wave-trains from c" to 

 about c lv . They were about one fringe in maximum amplitude at low speeds 

 in the absence of marked resistance in the telephone circuit; but above c'", 

 10,000 ohms had to be inserted to reduce the waves from broken (gaps, fig. 87) 

 to continuous forms. 



At certain very definite frequencies, however, marked disturbances showed 

 themselves. Thus at d" there was resonance and the field became filled with 



