Aug. lo, 1876] 



NATURE 



19 



thrown in the path of the determinations by the gradual fading 

 away of the watch-ticks as they approach coincidence with the 

 clock-ticks ; and, secondly, the impossibility of arriving at any 

 result at all, if the slightest noise (the rustle of a gentle breeze, 

 the piping of frogs, the bark of a distant dog) should fall 

 on the ear of the observer when engaged in making an experi- 

 ment. The general result of the numerous experiments thus 

 made shows that the sensation of the watch-tick is obliterated by 

 a CO ncident tick of the clock, when the intensity oT the clock- 

 tick is three times that of the watch-tick. This result, however, 

 must be regarded as merely approximative, not only from the 

 manner in which it was obtained, but from the complexity of the 

 sounds on which the experiments were made. It is interesting, 

 however, both as being, I believe, the first determination of this 

 kind that has ever been made, and as having opened out a new 

 and important field of research in physiological acoustics. 



Expa-imeuts on Musical Sounds. — Reserving the further deve- 

 lopment of my discoveries to a future paper, I will now briefly 

 describe some of the more prominent and simple phenomena, 

 which I discovered in experimenting with musical sounds. At 

 the outset I will remove an objection always made by those 

 versed in acoustics, but unacquainted with these new phenomena. 

 It is as follows : — " You say that one sound may obliterate the 

 sensation of another ; but are you sure that the real fact is not 

 an alteration of the quality of the moie intense sound by the 

 action of the concurrent feebler vibration?" I exclude this 

 objection by experimenting as follows : — An op;n or c'osed 

 organ-pipe is sounded forcibly, and at a few feet from it is placed 

 the instrument emitting the sound to be obliterated, which may 

 be either a tuning-fork on its resonance box, or a closed organ- 

 pipe communicating with a separate bellows. Suppose that in 

 the following experiment both tuning-fork and closed organ-pipe 

 produce a note higher in pitch than the more intense or extin- 

 guishing sound of the open organ-pipe. Now sound the fork 

 alone strongly, and alternately shut and open its resonance box 

 with the hand. We can thus obtain the sound of the fork in a 

 regular measure of time. When the ear has well apprehended 

 the intervals of silence and of sound thus produced, begin the 

 experiment by sounding the open pipe and tuning-fork simul- 

 taneously. Now, if any change is thus effected in the quality of 

 sound emitted by the open pipe, this change cannot occur except 

 when the pipe is sounding, ai.d hence, if it occurs at all, it must 

 occur in the regular measure in which the fork is sounded. The 

 following are the facts really observed. At first every time that 

 the mouth of the box is open, the sound of the fork is distinctly 

 heard, and changes the quality of the note of the open pipe. But 

 as the vibrations of the fork run down in amplitude, the sensa- 

 tions of its effect become less and less, till they soon entirely 

 vanish, and not the slightest change can be observed in the 

 quality or intensity of the note of the open organ-pipe, whether 

 the resonance box of the fork be open or closed. Indeed at this 

 stage of the experiment the vibrations of the fork may be sud- 

 denly and totally stopped without the ear being able to detect 

 the fact. But if instead of stopping the fork when it becomes 

 inaudible, we stop the sound of the open organ-pipe, it is impos- 

 sible not to feel surprised at the strong sound of the fork which 

 the open pipe had smothered and had rendered powerless to 

 affect the ear. If we replace the tuning-fork by a closed organ- 

 pipe of the same pitch, the results will be the same, but in this 

 case I adjust the intensity of the higher closed pipe to the point 

 of extinction by regulating the flow of air from the bellows, by a 

 valve worked with a screw. The alternation of sound and 

 silence is obtained by closing and opening the mouth of the 

 closed pipe by the hand. 



High Sounds cannot obliterate Low Sounds.— S. new and re- 

 markable fact was now discovered. No sound, even when very 

 intense, can in the slightest degree diminish or obliterate the 

 sensation of a concurrent sound which is lower in pitch. This 

 was proved by experiicents similar to the last, but differing in 

 having the more intense sound higher (instead of lower) in pitch. 

 In this case, when the ear decides that the sound of the (lower 

 and feebler) tuning-fork is just extinguished, it is generally dis- 

 covered on stopping the higher sound, that the fork, which 

 should produce the lower sound, has ceased to vibrate. This 

 surprising experiment must be made in order to be appreciated. 

 I will only remark that very many similar experiments have been 

 made, ranging through four octaves, and have been observed by 

 a score of different ears, with the same invariable result. It is 

 important to understand that this phenomenon depends solely on 

 the difference of pitch, and not at all on the absolute pitch of the 

 notes. Thus a feeble c'" (1024 double vibrations) is heard as 



distinctly through au intense e" (1280 double vibration^) as a 

 feeble ^ (128 double vibrations) is heard through an intense g 

 (192 double vibrations) or an intense c' (256 double vibrations). 



The development of the applications and of the further illustra- 

 tions of these discoveries would occupy too much space ; I mu-^t 

 therefore restrict myself to mentioning some of the most inter- 

 esting. Let a man read a sentence over and over again with the 

 same tone and modulation of voice; and while he is so doing 

 forcibly sound a c pipe (256 double vibrations). A remarkable 

 effect is produced, which varies somewhat with the voice experi- 

 mented on, but the ordinary result is as follows. It appears as 

 though two persons were reading together, one with a grave 

 voice (vvhich is found by the combination of all the real reader's 

 vocal sounds below c in pitch, or having less than 256 double 

 vibrations), the other with a high-pitched voice, generally squeaky 

 and nas.il, and, 1 need not add, very disagreeable. Of course 

 the aspirates come out with a distressing prominence. I have 

 observed many curious illustrations of this change in the quality 

 of the tone of the vo'ce, caused by the entire or partial oblitera- 

 tion of certain vocal components, while listening to persons 

 talking during the sound of a steam -whistle, or in one of our 

 long, resonant American railway carriages. Experiments similar 

 to those on the human voice, can be made, with endless modili- 

 cations, on other composite sounds, as those of reed-pipes, of 

 stringed instruments, of running water, &c. With one of my c 

 (128 double vibrations) free Grenie reeds, I get very marked 

 results. Using as a concurrent sound an intense c (256 double 

 vibrations) I perceive the prime or fundamental simple tone c to be 

 unaffected in intensity, while all the other partial tones (higher 

 harmonies or overtones, as they are sometimes called) are 

 almost obliterated, except the fifth partial (or fourth upper 

 partial) e", of 640 double vibrations, and the sixth partial (or 

 fifth upper partial) q' (of 768 double vibrations), which come out 

 with wonderful distinctness. The fact that the lowest, or prime 

 partial tone in the majority of ordinary compound musical tones 

 is the strongest, is due (among other reasons) to the fact that the 

 sensation of each partial tone of which the whole musical tone is 

 composed, is diminished by the action on the ear of all the com- 

 ponents or partial tones, below it in pitch. Thus the higher the 

 pitch of any component or partial tone, the greater the number 

 of lower components which tend to obliterate it. But the prime, 

 or lowest component partial tone, is not afTected by any other. 

 Another illustration I cannot resist giving. At the end of the 

 street in New York, in which I now reside, there is a large fire- 

 alarm bell, the residual sound of which, after its higher com- 

 ponents have disappeared, is a deep simple tone. This bass 

 sound holds its own with total indifference to the clatter of 

 horses, or to any sounds above it in pitch. It dies out with a 

 smooth gradient, generally without the slightest indentation or 

 break produced by the other sounds of the street. Indeed in 

 this case, as in all others where one sound remains unaffected by 

 intense higher notes, the observer feels as though he had a special 

 sense for the perception of the graver sound — an organ entirely 

 distinct from that which receives the impress of the higher tones. 



That one sonorous sensation cannot interfere with another 

 which is lower in pitch, is a remarkable physiological discovery, 

 and next after the demonstration of the fact that the ear is capable 

 of analysing compound musical sounds into their constituent or 

 partial simple tones, is probably the most important addition 

 yet made to our knowledge of the nature of hearing. It cannot 

 fail to introduce profound modifications into the hypotheses 

 heretofore framed respecting the mechanism and functions of the 

 ear. 



Application to Orchestral Performances. — We have seen how 

 an intense sound may obliterate, entirely or in part, the sensa- 

 tions of certain partial tones or components of any musical tone, 

 and thus produce a profound change in its quality. In a large 

 orchestra I have repeatedly witnessed the entire obliteration of 

 all sounds from violins, by the deeper and more intense sounds 

 of the wind instruments, the double-basses alone holding their 

 own. I have also observed the sounds of the clarinets lose their 

 peculiar quality of tone and consequent charm from the same 

 cause. No doubt the conductor of the orchestra heard all his 

 violins, ranged as they always are close around him, and did not 

 perceive that his clarinets had lost that quality of tone on which 

 the composer had relied for producing a special character of ex- 

 pression. 



The function of the conductor of an orchestra seems to be 

 threefold. First, to regulate and fix the time. Secondly, to 

 regulate the intensity of the sounds produced by the individual 

 instruments, for the purpose of expression. Thirdly, to give the 



