OP ARTS AND SCIENCES. 235 



from z \^ of a second to ^\^ of a second. With a duration of cur- 

 rent of T i 5 of a second, the free vibration often lasted as long as 

 T i 5 of a second. Under these circumstances the curve frequently 

 showed clearly the character and rate of the free vibration of the 

 diaphragm. 



It is uncertain whether it will be possible to study the duration 

 of tbe motion of the diaphragm by employing such currents as are 

 ordinarily used in telephony, as the effect of these is so slight. In 

 such a research it may prove advantageous to employ two tele- 

 phones in circuit, each furnished with a mirror, and giving a 

 fragment of a Lissajous curve when a beam of light is succes- 

 sively reflected from the mirrors, the momentary current being 

 sent through the telephones by the circuit-making wheel; or a 

 telephone with an objective carried by its diaphragm might be 

 substituted for the fork of the comparator. 



Two other methods have occurred to us of investigating the sub- 

 ject under consideration, which we hope to be able to make use of. 

 The first of these is to employ the wave siren of Koenig, using a 

 disk possessing only a single undulation of the sinusoid, or a frac- 

 tion of an undulation; or, for repeated sounds, an ordinary disk 

 with only a definite fractional part of the undulations exposed to 

 the action of the jet of air. Or perhaps the same result may be ob- 

 tained by the use of a narrower slit than that ordinarily employed, 

 so that the air jet shall cover only a portion of the sinusoid. 



The second method is to employ a phonograph, on the wax cylin- 

 der of which are impressed sinusoidal undulations produced by the 

 sound of a tuning-fork. If only a single such undulation, or por- 

 tion of an undulation, is allowed to remain, after removing the 

 others by paring away the wax, the diaphragm will necessarily ex- 

 ecute only a single harmonic vibration, or fraction of a vibration, 

 when the cylinder is rotated in the ordinary manner. 



Rogers Laboratory of Physics, 

 May, 1892. 



