196 





a,s, b, Cj, cSj 4 d^^ Cj /"i f.s.^ g^ g\ a^ as^ *, Cj c.s^ d^ d,s^ e. 



Fig. 1. Relative intensity of sound 

 of a technical micro-telephone 

 apparatus noted tone for tone, 

 (max. amplitude called 100). 



Tt will be seen that the discant of tiie speech zone is more inten- 

 sified than the bass. 



The sonnd conveyed to 

 the mirror by the tele- 

 phone is more intense 

 than that caught up by 

 the microphone. So the 

 circuit appears to intensify 

 the sound. Aw increment 

 of the available acoustic 

 energy results from a 

 decrement of the energy 

 afforded by the accumu- 

 lator. By elaborate expe- 

 rimentation this reinforce- 

 ment can be determined directly. It may also be promptly done in 

 a rough and ready way, if a second measuring mirror apparatus 

 is put in operation. 



This additional apparatus is provided with the trumpet of a 

 dictating phonograph. It is so sensitive that, even though the scale 

 be placed at Vs "^- ^'^'j '^"^ though a diaphragm of a phonograph 

 has been inserted, a unit of the scale represents one millierg of 

 acoustic energy per second. Such an instrument is competent to 

 register the amplitudes of whispers even, let alone those of spoken 

 \A ords. 



In a series of experiments carried out with Dr. Reuter I invari- 

 ably used 16 monosyllabic words of the sort called isozonal and 

 aequi-intonse, because their component speechsounds fulfil certain 

 requirements. We are now in a position to utter these words twice, 

 once with and once without a micro-telephone. The difference in the 

 amplitudes can then be noted. In both cases the intensity of our 

 voice can be registered on the scale, which is furnished \vith a 

 trumpet and is placed by the side of it. It appears then, that the 

 words spoken with a micro-telephone produce on an average ampli- 

 tudes exceeding 20 to 30 times those produced without insertion 

 of the electric circuit, which exalts the acoustic energy. 



The reinforcement recorded here, occurs with either apparatus of 

 tiie technique. It is remarkable that, as regards tone-selection, the 

 latter are so constructed as to reinforce the discant of the speechzone 

 more than the bass. It seemed to me, that a greater variety should 

 be aimed at in this respect. I, therefore, combined the microphones 

 and the telephones that were at my hand, in order to obtain this 



