OP ARTS AND SCIENCES. 75 



considered the subject. While with the latter it is more easy to pro- 

 duce an actual break of contact between the electrodes than with the 

 former when the sound is increased, on the other hand the quality is 

 much more satisfactorily reproduced, and does not so rapidly disap- 

 pear on increasing the loudness. These differences were clearly no- 

 ticed in the observations. Thus for slight excursions of the hammer 

 electrode the quality of the sound with two carbon electrodes was 

 found to be less satisfactory than when the hammer was of platinum, 

 although in the latter case the point of actual breaking of circuit and 

 sparking was usually reached with a less excursion than in the former 

 one. Evidence of these differences appears in the tables just given, 

 and also in those which follow. 



It must be observed, that, while the figures given in the tables show 

 what is the maximum amplitude of vibration of the electrodes con- 

 sistent with the transmission of quality, they entirely fail to indicate 

 the excessive minuteness of the least excursions which are capable of 

 this result. Plow minute these sometimes are may be inferred from 

 the following observation. 



With a microphone having a somewhat heavy anvil electrode, the 

 organ-pipe was gradually moved away from the diaphragm, and the di- 

 minishing range of motion of the electrodes noted in the usual manner. 

 When the pipe was at a distance of three inches the motion of the elec- 

 trodes was too slight to be visible, although this could have been seen 

 readily with the low magnifying power employed if it had been as great 

 as 50 Jjy^ in. The pipe, still blown with the same loudness, was then 

 carried farther and farther away. At a distance of thirty-six feet, which 

 was the most distant point from the microphone in the room, the sound 

 of the pipe was still distinctly though faintly audible at the receiver 

 placed in circuit with the microphone, and in a distant apartment. 



The results shown in the preceding tables give an idea of the phe- 

 nomena observable with a microphone of the structure employed. In- 

 asmuch as the primary object of the measurements was to obtain some 

 idea of the actual value of the excursion of the electrode, the mass 

 and normal pressure of the electrodes were not particularly considered, 

 except that they were so adjusted as to give good transmission with 

 moderate loudness of the sound actuating the microphone. But it 

 would of course be expected that the numerical value of the relative 

 excursion of the electrodes corresponding to any given character of 

 sound would vary with the mass of the anvil electrode and with the 

 normal pressure between the electrodes. Two separate sets of obser- 

 vations were made to observe the effects of such variations by Messrs. 



