Experiments and Theory ef the Harp of Eolus, jtg 



•bftaclc may determine the ftring to refolve itfelf into fuch aliquot parts rather than any 

 others, yet the blaft may be too ftrong, or too weak to admit of fuch a part vibrating with 

 fufEcient ftrength to produce a found; however, if any note be produced in this cafe, it muft 

 either be that of this very aliquot part, or of fome of its own aliquot divifions; for the qb- 

 ftacle muft neceflarily determine one of thjs interfeftions of the equal indentures. 



Obfervation IV. When the blaft rifes or falls, we find the tone alfo gradually rife or fall: 

 becaufe, as the blaft rifes, it grows too ftrong to admit of the vibrations of the longer aliquot 

 parts ; the vibrations of the fliort aliquot parts, therefore, will predominate, and will gradually 

 ihorten, as the blaft rifes in ftrength. But in cafes of fudden variations in the ftrength of the 

 blaft, there will be alfo fudden traiifitions in the tones. 



Obfervatien V. We fometimes hear a chord confifttng of two or three Eolian notes ; be- 

 caufe the blaft, which is of fuch a degree of ftrength as to admit of the vibrations of certain 

 aliquot parts, may alfo admit of the vibrations of other parts, if they be not very different 

 in length ; for their vibrations will be performed in times not very different. But if the 

 length of thefe parts, and confequently their times of vibration, be very different, the blaft 

 that admits of the vibration of the one will prevent that of the other. Accordingly, in look- 

 ing over the foregoing table, we find that the chords confift of thofe notes which are pro- 

 duced by fuch diff^erent aliquot parts as are leaft unequal : thus, one chord confifts of Cand 

 E, which notes are produced by one fixth and one feventh of the ftring. Another chord 

 confifts of F and A, which are produced by one fourth and one fifth of the ftring. An- 

 other confifts of A, C, and E, which notes are produced by one fifth, one fixth, and one. 

 feventh parts of the ftring. 



It is alfo worthy of obfervation, that in long ftrings we never hear the original note and 

 its o£tave at the fame time ; becaufe, though they are the next aliquot parts, yet their dif- 

 ference is fo great, that the blaft which admits of the vibration of one of them, will obftruft 

 and prevent the other. It is only in the higher divifions of the ftring that the chords are 

 heard at all ; and the flacker the note, the more frequent arc the chords, for the reafons af- 

 figned above, namely, becaufe the different aliquot parts, in fuch cafes, approach nearer ta 

 equality. 



Obfervation VI. Eolian tones are often heard, which are not produced by any exadl fub- 

 multiple of the ftring ; but fuch notes are very tranfitory, and immediately vary their pitch,, 

 gradually falling or rifing to the notes next below or above them, which are produced by 

 exaft aliquot parts of the whole ftring. This arifes from the tranfition of the divifions of 

 the ftring from one number to another ; for during this tranfition, the parts of the ftringy 

 whofe vibrations produce the note, are gradually lengthening or fhortening. Thus, fuppofe 

 the Eolian tone was produced by one third of a ftring ; and that the breeze fo varies as to 

 caufe this tone to fall into the ocSave of the original note ; the points of quiefcence will 

 gradually fUn along the ftrings, and by fo doing will produce a more gradually flattening, 

 until it terminates in the odlave to the whole ftring. 



Difcords are alfo often heard from the unifon ftrings of this inftratnenti the caufe c^ thisi» 



9i&> 



